JPH04320497A - Self-lubricating composite material and its preparation - Google Patents

Abstract

PURPOSE:To provide a self-lubricating composite material which is excellent in lubricating property at high temperature in vacuo and also in mechanical properties, thermal resistance and corrosion resistance, and a process for producing the same. CONSTITUTION:The title material comprises 5-80vol.% of a granular lubricative material phase with grain diameters of 20-2,000mum, which is composed primarily of boron nitride, tungsten disulfide and graphite and the rest of a combined phase composed of a metal and an alloy. The composite material is produced by mixing and molding both the powders and then sintering the molded mixture at 700-1,300 deg.C. Thus, there can be obtained at lubricating material which is usable at high temperatures and in all sorts of atmosphere.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-lubricating composite material suitable for bearing materials or sliding materials used as various mechanical parts, and a method for producing the same.

0002

[Prior Art] Conventionally, sintered bodies made of lubricating substances such as tungsten disulfide, molybdenum disulfide, graphite, graphite fluoride, and calcium fluoride, and various metals and alloys have been used as self-lubricating materials. There is. Representative examples of these conventional self-lubricating materials include JP-A-53
-122059, JP-A-62-196351, etc.

A self-lubricating material consisting of a lubricating substance such as tungsten disulfide, molybdenum disulfide or graphite and a binder phase of various metals and alloys is a self-lubricating material consisting of a starting material powder as the lubricating substance and a starting material powder as the binder phase. The lubricating substance in the sintered body thus obtained reacts with the metal and alloy of the binder phase and changes to a non-lubricating substance, reducing the yield. There is a problem in that the bond strength is low due to poor wettability with metals or alloys, resulting in increased wear and decreased strength of self-lubricating materials, resulting in a significant reduction in service life. Furthermore, self-lubricating materials containing lubricating substances such as tungsten disulfide, molybdenum disulfide, or graphite oxidize and lose their lubricity when exposed to temperatures of 300° C. or higher in the atmosphere. Therefore, it is difficult to use it in the atmosphere at high temperatures.

0004

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems, and has a self-lubricating property with low friction coefficient and specific wear rate at high temperatures and in vacuum, and excellent mechanical properties. The purpose of this invention is to provide a composite material and a method for manufacturing the same.

[0005]

[Means for Solving the Problems] As a result of studying the reactivity and wettability between the lubricating substance and the metal and alloy of the binder phase in self-lubricating composite materials, the present invention has developed the composition of the lubricating substance, its size, and the like. The invention was completed by obtaining the knowledge that specific elements effectively affect the bonding properties of the binder phase with metals and alloys.

That is, the present invention provides a particle size of 20 μm or more containing boron nitride, tungsten disulfide, and graphite.
The present invention is a self-lubricating composite material characterized in that it contains 5% by volume or more and 80% by volume or less of a granular lubricating substance phase with a particle diameter of 000 μm or less, and the remainder consists of a binder phase of an iron-based alloy.

[0007] Boron nitride is a chemically stable substance and has the lowest coefficient of friction up to the highest temperature in the atmosphere. However, while it is chemically stable, it has poor wettability and bonding properties with metals and alloys, and so far there have been few self-lubricating composites of metals and alloys using boron nitride, and even if there are, it has poor wettability and bonding properties with metals and alloys. It had low strength and could not be used. In addition, tungsten disulfide easily reacts with metals and alloys,
During sintering, it transformed into a substance with no lubricity, and its yield in metals and alloys was extremely low. As a result of a detailed study of the wettability and reactivity between the lubricating substance and the metal or alloy of the binder phase, it was found that the problem could be solved by adding graphite. That is, when a granular lubricating phase containing boron nitride, tungsten disulfide, and graphite is mixed with metal and alloy powder, molded, and then sintered,
Graphite preferentially dissolves in metals and alloys to firmly bond boron nitride with metals and alloys, and at the same time prevents tungsten disulfide from reacting with metals and alloys and changing into a substance with no lubricity. announced that it would. In this way, it is possible to produce a sintered body that has high mechanical strength and excellent lubricity in all atmospheres from air to vacuum, and even at high temperatures.

[0008]

[Function] The self-lubricating composite material of the present invention has a structure in which a phase containing a lubricating substance as a main component is surrounded by a binder phase of metals and alloys, so the strength of the sintered body is high. During use, the material is supplied as a film to the contact surface with the mating material, thereby significantly reducing both the specific wear rate and the coefficient of friction at high temperatures in the air or vacuum.

That is, the self-lubricating composite material of the present invention contains a granular lubricating material phase whose main components are boron nitride, tungsten disulfide, and graphite and has a particle size of 20 μm or more and 2000 μm or less, in an amount of 5% by volume or more and 80% by volume. Including % or less,
characterized in that the remainder consists of a binder phase of metals and alloys,
The granular lubricant phase contains boron nitride, tungsten disulfide, and graphite each in an amount of at least 3% by volume, and the binder phase contains at least one of iron-based alloy, nickel-based alloy, cobalt-based alloy, titanium-based alloy, etc. It consists of seeds.

[0010] If the volume occupied by the granular lubricating phase, which is mainly composed of boron nitride, tungsten disulfide and graphite and has a particle size of 20 μm or more and 2000 μm or less, is less than 5%, it will not be able to exhibit lubricity at high temperatures and in vacuum. , conversely, the sum of volumes is 8
If it exceeds 0%, the strength of the sintered body decreases, making it difficult to form a composite material. Therefore, the proportion of the granular lubricating phase is 5
% by volume or more and 80% by volume or less. If the size of the granular lubricating phase, which is mainly composed of boron nitride, tungsten disulfide, and graphite, is less than 20 μm, it will have poor dispersibility and will react with the binder phase, increasing the friction coefficient of the composite material and making it difficult to lubricate. If the thickness exceeds 2000 μm, the thickness of the binder phase increases and the coefficient of friction increases. For this reason, the size of the particulate lubricating material phase is set to 20 μm or more and 2000 μm or less. If boron nitride, tungsten disulfide, and graphite each occupy less than 3% of the volume in the granular lubricity phase, boron nitride's characteristic high-temperature lubricity and tungsten disulfide's characteristic lubricity in vacuum are Lubricity cannot be achieved. Furthermore, although graphite itself has lubricating properties, if it is less than 3%, it weakens the bonding force between boron nitride and metals and alloys, and at the same time it becomes impossible to prevent the reaction between tungsten disulfide and metals and alloys. Therefore, it is desirable that the volume occupied by boron nitride, gsten disulfide, and graphite be 3% or more.

[0011] The binder phase surrounding these lubricant material phases holds the lubricant material phase, suppresses deterioration and disappearance of the lubricant material phase during sintering, and forms a strong bond with the lubricant material. be. This bond can have various configurations depending on the composition of the lubricating material phase and the environment of use. When corrosion resistance and heat resistance are required, iron-based alloys such as carbon steel, alloy steel and stainless steel, nickel-based alloys such as Inconel and Hastelloy, cobalt-based alloys such as Stellite, and T
A titanium alloy such as i-6Al-4V or the like can be used as the binder phase.

In the method for producing the self-lubricating composite material of the present invention, a commonly used granulation method can be used for the granulation step to form a granular phase. For example, a mixed powder mainly composed of a lubricating substance is granulated in a rotating drum while adding water, alcohol, ethyl silicate, water glass, etc., or a mixed powder mainly composed of a lubricating substance is granulated. This method includes pressure molding, followed by crushing and granulation. After granulation, heat treatment at 500 to 1200°C in a non-oxidizing atmosphere can drive out gases contained in the raw material powder, and also makes the granulated powder harder and easier to handle. It is preferable.

[0013] The method for producing the self-lubricating composite material of the present invention includes:
The main components are boron nitride, tungsten disulfide, and graphite, and it consists of powder of a granular lubricating substance with a particle size of 20 μm or more and 2000 μm or less, and at least one of iron-based alloys, nickel-based alloys, cobalt-based alloys, titanium-based alloys, etc. The alloy powder for forming a binder phase is mixed and formed, and then sintered at a temperature of 700° C. or higher and 1300° C. or lower in a non-oxidizing atmosphere. If the temperature is less than 700°C, sintering will hardly progress, and if it exceeds 1300°C, the lubricating substance will decompose or change in quality.
The temperature shall be 300℃ or less. A non-oxidizing atmosphere is desirable since the lubricating substance will be oxidized in an oxidizing atmosphere.

[0014]

[Example] A granular lubricating solid phase powder containing boron nitride, tungsten disulfide, and graphite as the main components and having a particle size of 20 μm to 2000 μm, iron powder as a binder phase, and powder of metals and alloys such as stainless steel is milled in a ball mill. After mixing using a press molding machine at a pressure of 3 tons/cm2, a green compact was produced. After sintering the compact in vacuum, a tensile test and a friction and wear test were conducted.

[0015] A test piece of 3 x 2 x 30 mm was used for the tensile test. The coefficient of friction was measured using a disc-shaped sample with SUS304 as the mating material, at a speed of 60 m/min, and a surface pressure of 50 kg/cm.
2, and the specific wear rate was determined under the conditions of a surface pressure of 100 kg/cm2 and a friction distance of 500 m. The coefficient of friction in vacuum is 10-5
It was measured at a vacuum degree of torr.

Table 1 shows the particle size, blending amount and composition of the granular phase mainly composed of the lubricating substance of the present invention, as well as the composition and manufacturing conditions of the binder phase. Table 2 shows the tensile strength, friction coefficient, and specific wear rate of the sintered body. The compositions, manufacturing conditions, and characteristics of the sintered bodies of comparative examples other than those of the present invention are also listed in Tables 1 and 2.

The products of the present invention are sample numbers 1 to 3, and are examples in which the binder phase is an iron alloy, a nickel alloy, or a titanium alloy. The material of the present invention has a tensile strength of 20 kg/mm2 or more,
It is a self-lubricating composite material with a friction coefficient of 0.2 or less in air and vacuum, and excellent in both strength and lubricity. Comparative examples deviating from the present invention are shown in sample numbers 4 to 6. Since sample number 4 does not contain graphite, sample number 6 has a small coefficient of friction but a low strength of the sintered body. Sample No. 5 does not contain WS2 and therefore has a large friction coefficient in vacuum. Sample No. 6 contains a small amount of lubricant, so although its strength is high, its friction coefficient and specific wear rate are both high.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Effects of the invention] The self-lubricating composite material of the present invention has a low coefficient of friction and a low specific wear rate, and has excellent mechanical properties, and can be used at high temperatures and harsh environments that were previously unusable. It is a revolutionary material.

Claims (4)

[Claims] [Claim 1] Particles containing boron nitride, tungsten disulfide, and graphite as main components with a diameter of 20 μm or more and 2000 μm
A self-lubricating composite material comprising 5% by volume or more and 80% by volume or less of the following particulate lubricating material phase, with the remainder consisting of a binder phase of metal and alloy. 2. The self-lubricating composite material of claim 1, wherein the particulate lubricating phase contains at least 3% by volume of each of boron nitride, tungsten disulfide, and graphite. 3. The self-lubricating composite material according to claim 1, wherein the binder phase comprises at least one of an iron-based alloy, a nickel-based alloy, a cobalt-based alloy, and a titanium-based alloy. 4. After mixing and molding granular powder containing boron nitride and tungsten disulfide and having a particle size of 20 μm or more and 2000 μm or less and an alloy powder for forming a binder phase, the mixture is heated at 700° C. in a non-oxidizing atmosphere. A method for producing a self-lubricating composite material, characterized in that sintering is performed at a temperature of 1300°C or less.