JP5712919B2 - Low friction sliding member - Google Patents

Description

  The present invention relates to a sliding member having excellent sliding characteristics, particularly friction characteristics and wear resistance in the presence of an organic molybdenum-containing lubricant.

  In automobiles, sliding members are used in various devices such as engines and transmissions, and various developments have been made in order to improve the sliding characteristics of such sliding members. Reducing the coefficient of friction of the sliding member is particularly important because it leads to an improvement in the fuel consumption of the automobile. In recent years, a technique for coating a diamond-like carbon film (also referred to as a DLC film or an amorphous carbon film) has been used as a coating technique for the surface of a sliding member in order to reduce the friction coefficient and improve the wear resistance. Attention has been paid. Various attempts have been made to form diamond-like carbon films in order to obtain excellent sliding properties.

  For example, Patent Documents 1 to 3 disclose DLC films containing molybdenum (Mo), tungsten (W), or chromium (Cr). In Patent Document 4, a DLC film containing hydrogen is formed on the sliding surface of a swash plate of a swash plate compressor, and silicon or nitrogen is added to the DLC film, or a molybdenum disulfide film is formed on such a swash plate. It is disclosed that good sliding characteristics can be obtained by forming the like. Patent Document 5 includes at least one of silver (Ag), magnesium (Mg), indium (In), tin (Sn), silicon (Si), zirconium (Zr), copper (Cu), molybdenum (Mo), and A sliding member having a DLC film containing tungsten (W) and sulfur (S) is disclosed.

JP-A-62-116749 JP 62-116750 A JP-A-62-116751 JP 2001-280236 A JP 2007-177313 A

  The sliding member is often slid in the presence of a lubricant, and a lubricant containing an organic molybdenum compound such as molybdenum dithiocarbamate as an additive is known. When such a lubricant is used, a molybdenum compound layer is formed on the surface of the sliding member and friction is reduced. However, when a lubricant containing an organomolybdenum compound is used for a sliding member provided with a DLC film, the surface of the sliding member is oxidized, resulting in a decrease in wear resistance and seizure resistance. There is.

  In recent years, the high performance of automobile engine parts due to high output and high rotation is remarkable. In sliding parts used in engines, there is a limit in improving the performance of the sliding member alone, and it is required to provide excellent sliding characteristics by an optimal combination of the sliding member and the lubricant.

The present inventor has excellent friction characteristics and wear resistance in sliding using an organic molybdenum-containing lubricant by forming a DLC film containing at least one of platinum (Pt) and rhodium (Rh) on the sliding surface. It was found that a sliding member was obtained. The gist of the present invention is as follows.
(1) A sliding member for sliding using an organomolybdenum-containing lubricant, comprising a diamond-like carbon film containing a metal that is at least one of Pt and Rh on a sliding surface.
(2) The sliding member according to (1), wherein the diamond-like carbon film contains 0.25 to 10 at% of the metal.
(3) The sliding member according to (1) or (2), wherein the diamond-like carbon film contains 0 to 35 at% hydrogen.
(4) The sliding member according to any one of (1) to (3), wherein the lubricant contains 50 to 1500 ppm of an organic molybdenum compound.
(5) The sliding member according to any one of (1) to (4), wherein the metal is dispersed in the diamond-like carbon film in a cluster state having a size of 200 nm or less.
(6) A sliding member comprising a sliding member provided with a diamond-like carbon film containing a metal that is at least one of Pt and Rh on the sliding surface, and an organic molybdenum-containing lubricant supplied to the sliding surface. And a combination of lubricants.

  The sliding member of this invention can suppress the oxidation of the DLC film resulting from the organic molybdenum compound-derived component, when the DLC film contains at least one of Pt and Rh. Therefore, the sliding member of the present invention is excellent in sliding characteristics, particularly friction characteristics and wear resistance in sliding using the organic molybdenum-containing lubricant.

  In the present invention, the sliding member means a mechanical part having a sliding part, and specifically includes a wet clutch, an engine piston, a gear, a spline, a plain bearing, a valve operating system part, and the like. The sliding member of the present invention is intended to slide under wet conditions using an organic molybdenum-containing lubricant. The sliding member of the present invention is particularly suitable for use in a cylinder bore and piston ring for an internal combustion engine or a cylinder and piston type sliding part of a fuel injection part.

  The base material of the sliding member of the present invention is not particularly limited as long as it is a sliding part of various devices, and may be any of a metal base material, a ceramic base material, a resin base material, etc. It is preferably made of metal. As the metal constituting the base material, an aluminum alloy containing Cu, Mg, Zn and the like in addition to cast iron, steel and aluminum, a copper alloy containing Zn, Al, Sn and the like in addition to copper are preferable.

  The sliding member of the present invention is characterized in that a DLC film containing at least one of Pt and Rh is provided on the sliding surface. The DLC film may contain only one of Pt and Rh or both Pt and Rh. A sliding member having a DLC film containing at least one of Pt and Rh on the sliding surface is very thin Pt or Dt on the outermost surface of the DLC film even when used in the presence of an organic molybdenum-containing lubricant. It is considered that an Rh film is formed, which suppresses the reaction of molybdenum trioxide resulting from the organomolybdenum compound with the DLC film, so that deterioration due to oxidation of the DLC film is unlikely to occur. Therefore, in the sliding member of the present invention, excellent sliding characteristics, particularly friction characteristics and wear resistance can be obtained even when an organic molybdenum-containing lubricant is used. Accordingly, the present invention provides a sliding member comprising a sliding member having a DLC film containing a metal that is at least one of Pt and Rh on the sliding surface, and an organic molybdenum-containing lubricant supplied to the sliding surface. Also related to the combination of lubricants.

  The content of the metal, which is at least one of Pt and Rh, in the DLC film is preferably in the range of 0.25 to 10 at%, particularly 0.3 to 9 at% in terms of atomic percentage (at%). Here, the atomic percentage means the percentage of the composition element in the material (in this case, the DLC film) on the basis of the number of atoms. If the metal content is too large, the hardness and strength of the DLC film are lowered, and the sliding characteristics are also lowered. On the other hand, if the metal content is too small, the effect of improving the sliding properties due to the addition of the metal is not observed, but this is not the case within the above range.

  In the DLC film in the sliding member of the present invention, the metal that is at least one of Pt and Rh is dispersed in the film in a cluster state. The size of the cluster is preferably 200 nm or less, particularly 150 nm or less, and particularly preferably 100 nm or less. If the size of the cluster is within such a range, the hardness and strength of the DLC film will not be reduced.

  The DLC film may further contain hydrogen (H). A sliding member having a DLC film containing hydrogen on the sliding surface has particularly low friction. The amount of hydrogen in the DLC film is preferably in the range of 0 to 35 at%, particularly 5 to 25 at% in terms of atomic percentage (at%).

  The DLC film can be formed by a known CVD method (chemical vapor deposition method) or PVD method (physical vapor deposition method), for example, a plasma CVD method, an ion plating method, a sputtering method, or the like. The DLC film in the sliding member of the present invention is, for example, a PVD method in which a solid material is vaporized by a physical action to form a film on the surface of a substrate, particularly a metal target and a carbon target made of Pt or Rh It can be formed by a sputtering method in which atoms and molecules on the target surface are released by irradiating an inert gas such as argon accelerated by an electric field. At that time, a DLC film containing hydrogen can be formed by introducing a hydrocarbon gas such as methane or acetylene as a raw material gas together with an inert gas and decomposing the hydrocarbon gas by discharge.

  The organomolybdenum-containing lubricant used for the sliding member of the present invention preferably contains an organomolybdenum compound in an amount of 50 to 1500 ppm, particularly 200 to 1200 ppm, based on mass. If the content of the organomolybdenum compound is too small, the effect of reducing the friction coefficient is not so much seen. On the other hand, if the content is too large, the decrease in the friction coefficient is saturated (it does not fall below a certain value), and the Although a problem occurs in dispersion, such a problem does not occur within the above range.

  Examples of the organomolybdenum compound contained in the organomolybdenum-containing lubricant include molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and molybdenum amine complex, among which MoDTC and MoDTP are preferable.

  MoDTC is preferably molybdenum dialkyldithiocarbamate sulfide or sulfurized oxymolybdenum dialkyldithiocarbamate. In these organic molybdenum compounds, the alkyl group is preferably a branched or straight chain alkyl group having 4 to 18 carbon atoms, and specifically, a butyl group, a 2-ethylhexyl group, an isotridecyl group, a stearyl group, or the like is preferable. The alkyl groups present in one molecule may be the same and different.

  MoDTP is preferably molybdenum sulfide dialkyldithiophosphate or sulfurized oxymolybdenum dialkyldithiophosphate. In these organic molybdenum compounds, the alkyl group is preferably a branched or straight chain alkyl group having 4 to 18 carbon atoms, and specifically, a butyl group, a 2-ethylhexyl group, an isotridecyl group, a stearyl group, or the like is preferable. The alkyl groups present in one molecule may be the same or different.

  In addition to organic molybdenum compounds as friction modifiers, organic molybdenum-containing lubricants are additives that are used in ordinary engine oils, such as antioxidants, detergent dispersants, viscosity index improvers, rust inhibitors, and antifoaming agents. , Oiliness improvers, extreme pressure additives and the like may be included.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to these Examples.

Example 1
A 16 mm × 6 mm × 10 mm dice test piece (surface roughness 0.1 μmRa) was prepared from a rod of stainless steel (JIS standard SUS440C, quenched product, surface hardness Hv500). An unbalanced magnetron sputtering method (one graphite target and one Pt target, flow gas: argon containing 5% methane, bias voltage: 100V on the graphite side, 80V on the Pt side, temperature 100) C.) was used to form a DLC film having a thickness of 1.5 μm. The formed Pt-containing DLC film had a surface roughness of 0.12 μmRa, a hardness of Hv2000, a Pt amount of 4 at%, a Pt cluster size of 50 nm, and a hydrogen amount of 10 at%.

  On the other hand, a cylindrical test piece having an outer diameter of 35 mm, an inner diameter of 30 mm, and a width of 10 mm was manufactured using stainless steel (JIS standard SUS440C) as the mating sliding member (surface roughness 0.2 μmRa, surface hardness Hv380).

  The DLC film formation surface of the dice test piece and the outer peripheral surface of the cylindrical test piece were brought into contact with each other, and while supplying oil (SAE5W-30, containing MoDTC 700 ppm, oil temperature 80 ° C.), the cylinder test was performed at a load of 60 kgf and a rotation speed of 160 rpm. A wear test was performed in which the piece was rotated for 30 minutes. The wear amount of the dice specimen was measured as the wear scar depth, and the wear amount of the cylindrical specimen was measured as the wear weight. Further, the coefficient of friction after 30 minutes was measured.

(Example 2)
The same procedure as in Example 1 was performed except that the Pt amount in the DLC film of the dice test piece was 0.2 at%, 0.3 at%, 9 at%, and 12 at%.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that the Pt target was not used when the DLC film was formed on the dice test piece. The formed additive-metal-free DLC film had a surface roughness of 0.12 μmRa, a hardness of Hv2100, and a hydrogen content of 10 at%.

  The data obtained in Examples 1 and 2 and Comparative Example 1 are summarized in Table 1. When the addition amount of Pt in the DLC film was 0.3 at%, 4 at%, and 9 at%, the results were that the wear was particularly small and the friction coefficient was low.

(Example 3)
The same procedure as in Example 1 was performed except that the Rh target was used instead of the Pt target when the DLC film was formed on the dice test piece. The formed Rh-containing DLC film had a surface roughness of 0.12 μmRa, a hardness of Hv1800, an Rh amount of 4 at%, an Rh cluster size of 80 nm, and a hydrogen amount of 12 at%.

Example 4
The same procedure as in Example 3 was performed except that the Rh amount in the DLC film of the dice test piece was 0.2 at%, 0.3 at%, 9 at%, and 12 at%.

  The data obtained in Examples 3 and 4 and Comparative Example 1 are summarized in Table 2. When Rh was used instead of Pt, the same result as that obtained when Pt was used was obtained.

(Comparative Example 2)
The same procedure as in Example 1 was performed except that a Mo target was used instead of the Pt target when the DLC film was formed on the dice test piece. The formed Mo-containing DLC film had a surface roughness of 0.12 μmRa, a hardness of Hv1850, a Mo amount of 4 at%, a Mo cluster size of 70 nm, and a hydrogen amount of 11 at%.

(Comparative Example 3)
The same procedure as in Example 1 was performed except that a W target was used in place of the Pt target when the DLC film was formed on the dice test piece. The formed W-containing DLC film had a surface roughness of 0.12 μmRa, a hardness of Hv1900, a W amount of 4.5 at%, a W cluster size of 70 nm, and a hydrogen amount of 10 at%.

(Comparative Example 4)
The same procedure as in Example 1 was performed except that a V target was used instead of the Pt target when the DLC film was formed on the dice test piece. The formed V-containing DLC film had a surface roughness of 0.11 μmRa, a hardness of Hv1800, a V amount of 4 at%, a V cluster size of 80 nm, and a hydrogen amount of 11 at%.

(Comparative Example 5)
The same procedure as in Example 1 was performed except that a Ti target was used instead of the Pt target when the DLC film was formed on the dice test piece. The formed Ti-containing DLC film had a surface roughness of 0.13 μmRa, a hardness of Hv1900, a Ti amount of 4 at%, a Ti cluster size of 100 nm, and a hydrogen amount of 12 at%.

  The data obtained in Comparative Examples 1 to 5 are summarized in Table 3 together with the data of Examples 1 and 3. When Mo, W, V, or Ti was used in place of Pt, the friction coefficient slightly decreased, but the die specimen wear amount increased rather than that containing no added metal.

Claims (5)

It comprises a diamond-like carbon film containing R h on the sliding surface, sliding the Rh is dispersed in the diamond-like carbon film in the state of the cluster having a size of less than 200 nm, using an organic molybdenum-containing lubricant Sliding member for. The sliding member according to claim 1, wherein the diamond-like carbon film contains 0.25 to 10 at% of Rh .   The sliding member according to claim 1 or 2, wherein the diamond-like carbon film contains 0 to 35 at% of hydrogen.   The sliding member according to any one of claims 1 to 3, wherein the lubricant contains 50 to 1500 ppm of an organic molybdenum compound. It comprises a diamond-like carbon film containing R h on the sliding surface, wherein Rh is a sliding member which is dispersed in the diamond-like carbon film in the state of the cluster having a size of less than 200 nm, supplied to sliding surfaces A combination of a sliding member and a lubricant comprising an organic molybdenum-containing lubricant.