JP2011063839A - Sliding member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To constitute a sliding member so that wear resistance and low-friction property are obtained even under severe lubricating conditions. <P>SOLUTION: The sliding member is obtained by combining a first member and a second member having sliding surfaces which slide to each other. The sliding surface of the first member is formed with a plated film containing a Cr component, wherein the plated film is formed by electrolytic deposition from a plating bath containing the Cr-component and an organic sulfonic acid. The sliding surface of the second member is formed with silicon nitride. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sliding member excellent in wear resistance and low friction.

  It is known to form a Cr-containing plating film electrolytically deposited from a plating bath containing a Cr component and an organic sulfonic acid on a sliding surface of an automobile or other equipment in order to improve its wear resistance. . For example, in Patent Document 1, a CrMo plating film is formed on a workpiece using a plating bath containing an organic sulfonic acid, and 400 to 1300 cracks per 1 cm in length are formed on the plating film by etching treatment. In addition, it is described that the surface of the plating film is ground to form a low friction sliding surface with high lubricity. In Patent Document 2, when a CrMo plating film is formed on a work using a plating bath containing organic sulfonic acid, the amount of organic sulfonic acid is adjusted to adjust the (222) oriented crystal on the surface of the CrMo plating layer. It is described that the abundance ratio is 60% or more and 80% or less, and a plating film having wear resistance and low friction is obtained.

JP 2006-219756 A JP 2007-291423 A

  The sliding member is generally required to have wear resistance and low friction. For example, a sliding member of a piston or a valve train of an automobile engine has excellent wear resistance to ensure engine reliability. A low coefficient of friction is required to improve fuel efficiency. In the example of a rotary piston engine, a hard CrMo plating film is formed on the trochoid surface of the rotor housing that forms the working chamber, and chill cast iron is adopted for the apex seal that slides on the trochoid surface, so that the above requirements are met. To meet.

  However, while the hardness of the hard CrMo plating film is about HV1000, the hardness of the chill cast iron adopted for the apex seal is about HV650, so the lubrication conditions are severe, such as a very small amount of lubricating oil. In some cases, a phenomenon may occur in which the wear amount of the apex seal increases unilaterally.

  An object of the present invention is to configure a sliding member so as to obtain wear resistance and low friction even under severe lubrication conditions.

  In order to solve the above-mentioned problems, the present invention combines high-speed Cr plating and silicon nitride as sliding surface materials for two members that slide on each other.

  That is, one aspect of the present invention is a sliding member formed by combining a first member and a second member having sliding surfaces that slide on each other, and the sliding surface of the first member is Cr. It is formed of a plating film containing Cr formed by electrolytic deposition from a plating bath containing components and organic sulfonic acid, and the sliding surface of the second member is formed of silicon nitride.

  The Cr-containing plating film that forms the sliding surface of the first member is a so-called high-speed plating film formed by the organic sulfonic acid acting as a catalyst for increasing the plating deposition rate. This Cr-containing plating film has the same level of hardness as that of conventional hard Cr plating (about HV1000), but by adding organic sulfonic acid to the plating bath, the crystal face of the Miller index (222) becomes the film surface side. The abundance of (222) oriented Cr crystals (BCC) facing the surface increases, and the compressive residual stress also increases.

  Thus, since the sliding surface of the first member is formed by the Cr-containing plating film as described above, even if the sliding surface of the second member is formed of hard silicon nitride around HV1500, Less wear due to movement. Further, the sliding surface formed of silicon nitride of the second member is less worn because the sliding surface of the first member is formed of the Cr-containing plating film as described above. In addition, the combination of the Cr-containing plating film and silicon nitride improves the friction characteristics between the sliding surface of the first member and the sliding surface of the second member (lowering the friction coefficient).

  In a preferred embodiment, the plating film has a (222) oriented crystal whose surface (222) faces the surface side specified by X-ray diffraction analysis, and the presence rate on the surface of the plating film is 60% or more and 80% or less. It is.

  The (222) plane is a crystal plane in which Cr crystal atoms are packed most closely, and the crystal lattice spacing is the narrowest. Accordingly, the crystal distortion generated when an external force is applied by sliding relative to the silicon nitride sliding surface increases. For this reason, the plating film having a high abundance of (222) -oriented Cr crystals originally has a high compressive residual stress, but the degree of increase of the internal compressive stress by an external force is large.

  Thus, the oxidation of the Cr crystal is caused by the diffusion of oxygen from the Cr plating film surface to the inside, and as a result, a Cr oxide film is formed on the Cr plating film surface. However, in the Cr plating film having a high compressive stress as described above, since the crystal lattice spacing is narrowed, it is difficult for oxygen diffusion to occur. For this reason, the Cr oxide film produced in a normal use environment becomes thin, and the gradient of internal stress from the surface of the film to the inside becomes steep.

  As a result, at the time of relative sliding between the first member and the second member, the Cr oxide film is likely to be peeled off, or the Cr oxide film is cleaved inside, and the chip is likely to be partially chipped. In other words, the sliding resistance is reduced. That is, the Cr oxide film and silicon nitride partially adhere during sliding, and the shearing force required to peel the adhesion part from the Cr oxide film or Cr plating film becomes the frictional force. Since the Cr oxide film is thin and easily peels or cleaves, it acts as a solid lubricant and reduces the frictional force.

  In addition, when the abundance ratio of the (222) oriented crystals on the surface of the plating film exceeds 80%, the stress further increases, thereby acting to suppress the progress of oxidation. As a result, the thickness of the Cr oxide film formed on the sliding surface becomes excessively thin, and the lack of these oxide films increases as the material slides. In connection with this, since the exposure of the base plating film body becomes remarkable and causes adhesion of metals, it is not preferable.

  In order to form a Cr oxide film that is easily peeled off or easily cleaved as described above, the compressive residual stress of the Cr-containing plating film is preferably 20 MPa or more, and more preferably 40 MPa or more.

  The thickness of the Cr oxide film is preferably smaller than the average crystallite diameter of the (222) oriented crystal. That is, when the thickness of the Cr oxide film is approximately the same as or larger than the size of the (222) oriented crystallite, it means that the entire (222) oriented crystallite is oxidized. It is none other than. If so, the crystallites easily fall off during sliding, which causes excessive wear.

  However, the case where the thickness of the Cr oxide film is too thin as compared with the crystallite diameter is not preferable. This case occurs when the crystallite diameter is excessively large, which means that the Cr oxide film is bonded to a single crystallite in a wide area, and the Cr oxide film It becomes difficult to peel from the plating film, that is, the friction coefficient becomes large. Therefore, the Cr oxide film preferably has a thickness of, for example, 1/5 or more and less than 1/1 of the crystallite diameter.

  Another aspect of the present invention is a sliding member formed by combining a first member and a second member having sliding surfaces that slide on each other, wherein the sliding surface of the first member contains Cr and contains 20 MPa. It is formed by the plating film having the above compressive residual stress, and the sliding surface of the second member is formed by silicon nitride.

  That is, as described above, when the compressive residual stress of the Cr-containing plating film increases, the Cr oxide film generated in a normal use environment becomes thin, and the peelability or cleavage of the Cr oxide film increases. For this reason, in the combination of the sliding surface made of a Cr-containing plating film having a high compressive residual stress of the first member and the sliding surface made of silicon nitride of the second member, the wear of each sliding surface is small. Therefore, it is advantageous for securing low friction characteristics. The compressive residual stress of the Cr-containing plating film is more preferably 40 MPa or more. The upper limit of compressive residual stress is preferably 120 MPa.

  Such a Cr-containing plating film having a high compressive residual stress can be obtained by the high-speed plating method using the above-described organic sulfonic acid as a catalyst, but other catalysts such as fluoride are added to the plating bath to increase the deposition rate. Can also be obtained.

  The Cr-containing plating film that forms the sliding surface of the first member described above may be formed by CrMo alloy plating containing Cr as a main component in addition to the Cr polycrystal. Addition of Mo makes it possible to refine the crystal of the plating film, improve strength, and improve heat resistance, and is advantageous for improving lubricity, reducing friction (reducing the friction coefficient), and preventing seizure. The amount of Mo eutectoid is preferably 0.3% or more and 1.0% or less.

  According to the present invention, in the sliding member formed by combining the first member and the second member having sliding surfaces that slide relative to each other, the sliding surface of the first member is plated containing organic sulfonic acid. Since it is formed by a Cr-containing plating film formed by electrolytic deposition from a bath, or by a Cr-containing plating film having a compressive residual stress of 20 MPa or more, and the sliding surface of the second member is formed by silicon nitride, Wear of the sliding surfaces of the first member and the second member is reduced, and the friction characteristics are improved.

1 is a cross-sectional view schematically showing a rotary piston engine to which the present invention is applied. It is a figure which shows typically the structure of the Cr containing plating film surface part of the sliding member which concerns on this invention. It is a graph which shows the relationship between the (222) plane presence rate and internal stress of a Cr containing plating film. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure ((a) is a top view, (b) is a side view) which shows a frictional wear characteristic testing machine schematically. It is a graph which shows the pin height abrasion amount when a pin on disk friction abrasion test is done with the combination of various sliding surface materials. It is a graph which shows the amount of disk wear when performing a pin-on-disk friction and wear test with a combination of various sliding surface materials. It is a graph which shows a time-dependent change of a friction coefficient when a pin-on-disk friction abrasion test is done with the combination of various sliding surface materials.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the present invention, its application, or its use.

  FIG. 1 is a simplified diagram of a rotary piston engine according to an embodiment, and a trochoidal surface (sliding surface) 2 of a rotor housing 1 as a first member is mounted on each top of a rotor 4 that rotates an output shaft 3. The top surface (sliding surface) of the apex seal 5 as the second member is slid. In this engine, fuel containing oil is sucked into the working chamber 7 together with air from the intake port 6, and the fuel moved in the direction of the arrow 8 while being compressed as the rotor 4 rotates is ignited by the spark plugs 9 </ b> A and 9 </ b> B. A series of steps of expanding and exhausting from the exhaust port 10 after the output shaft 3 is rotated by the pressure of the combustion gas is repeated.

  The rotor housing 1 is manufactured by casting a liner made of, for example, a high-strength steel plate having a trochoidal surface 2 formed on an aluminum alloy. Since the apex seal 5 slides on the trochoidal surface 2, high heat resistance, wear resistance, and low friction are required. Therefore, a Cr-containing plating film is formed on the trochoid surface 2 by a high-speed plating method. On the other hand, the apex seal 5 is made of silicon nitride.

  FIG. 2 schematically shows a Cr-containing plating film 10, in which 11 is a (222) oriented Cr crystal whose (222) plane is directed to the film surface side specified by X-ray diffraction analysis, 12 Are other Cr crystals with different crystal orientations. On the surface of the Cr-containing plating film 10, a Cr oxide film 13 made of oxides 11 a and 12 a formed at the sites of (222) oriented Cr crystal 11 and other Cr crystals 12 is formed. The abundance of the (222) oriented Cr crystal 11 on the surface of the Cr-containing plating film 10 is 60% or more and 80% or less, and the Cr-containing plating film 10 has a compressive residual stress of 20 MPa or more.

  Such a Cr-containing plating film 10 can be formed by adjusting a plating bath and plating conditions.

<Method for forming Cr-containing plating film>
After containing a Cr component, sulfuric acid and organic sulfonic acid as a catalyst, and if necessary, a liner is put in a plating bath containing a Mo component and preheated to a predetermined temperature, and after cleaning the liner surface by reverse electric treatment for several minutes, A Cr-containing plating film is formed on the trochoidal surface by sequentially performing a strike plating process (positive electric process) for several minutes and a main plating process (positive electric process) for a predetermined time.

As the Cr component, anhydrous chromic acid CrO ₃ is preferable, and Cr ₂ O ₃ is added as necessary. As the Mo component, sodium molybdate or ammonium molybdate can be employed. The organic sulfonic acid is represented by HSO ₃ R, and R has an aliphatic hydrocarbon group having 10 or less carbon atoms such as a methyl group and an ethyl group, toluene having a methyl group at the para position, and an unsaturated hydrocarbon group. An aromatic hydrocarbon group in which an acyclic hydrocarbon is bonded to one aromatic ring such as styrene is preferable. R may be another aromatic hydrocarbon group or a plurality of sulfonic acid groups (HSO ₃ ). Specific examples include methanesulfonic acid and methanedisulfonic acid.

  The plating bath is, for example, 240 g / L to 280 g / L of chromic anhydride, 2.5 g / L to 3.3 g / L of sulfate ion, 10 ml / L to 35 ml / L of organic sulfonic acid, The amount of sodium molybdate may be 50 g / L or more and 65 g / L or less. The plating bath temperature is adjusted to, for example, 50 ° C. or more and 60 ° C. or less.

The current density of the reverse current treatment for cleaning is 50 A / dm ² or more and 60 A / dm ² or less, the current density of the strike plating treatment is 40 A / dm ² or more and 55 A / dm ² or less, and the current density of the plating treatment is 30 A / dm ^2. It may be 40 A / dm ² or less. The finish grinding is preferably performed by honing or the like so that the surface of the plating film is, for example, Ra 2.0 μm or less.

  The abundance of (222) -oriented crystals and compressive residual stress in the Cr-containing plating film can be adjusted by the amount of the organic sulfonic acid added.

  That is, when organic sulfonic acid is added to the plating bath, the plating deposition rate is increased, the abundance of (222) oriented crystals is increased, and the compressive residual stress is increased. This is because organic sulfonic acid has a strong polarity and is easily adsorbed on the workpiece surface, which makes the Cr precipitation point different from the conventional one, and the crystal orientation of the Cr-containing plating is (222) plane. It seems to work to increase. The higher the concentration of organic sulfonic acid, the higher the proportion of (222) oriented crystals. Along with this, the compressive residual stress of the Cr-containing plating film increases.

<Examples and Comparative Examples>
A CrMo plating film was formed on the surface of the steel workpiece by changing the amount of the catalyst (organic sulfonic acid) added in the plating bath. The plating bath composition is as shown in Table 1, and the amount of catalyst added was changed from 0 ml / L to 30 ml / L. As a catalyst, that is, organic sulfonic acid, Heef25-R manufactured by Atotech was used. The plating conditions are as shown in Table 2. In Table 2, “A / dm ² ” represents current density, and time represents processing time.

-Relationship between the amount of catalyst added and the abundance of (222) oriented crystals-
The abundance ratio of each crystal face facing the surface side of each CrMo plating film having a different catalyst addition amount was measured by X-ray diffraction analysis. The measurement was performed under conditions shown in Table 3 using an X-ray diffractometer RU-200 manufactured by Rigaku Corporation after finish grinding of the CrMo plated surface of the test material. The results are shown in Table 4.

    According to Table 4, in Examples 1 to 3 in which organic sulfonic acid was added as a catalyst, the abundance of (222) oriented crystals was higher (60% or more) than in Comparative Examples in which the catalyst was not added, In addition, as the amount of catalyst added increases, the abundance of (222) oriented crystals increases.

-Relationship between catalyst loading, internal stress and average crystallite size-
For each of Examples 1 to 3 and Comparative Example, the internal stress of the CrMo plating film after the grinding was measured by an X-ray stress measurement method. The measurement was performed under the conditions shown in Table 5 using a strain flex PSPC / MSF-2M manufactured by Rigaku Corporation. Regarding the average crystallite diameter of the CrMo plating film, Scherrer's formula (crystallite diameter D (hkl) = 0.9λ / (β _1/2 · cos θ) based on the X-ray diffraction pattern obtained by the X-ray diffraction apparatus. ), Where hkl is the Miller index, λ is the characteristic X-ray wavelength (angstrom), β _1/2 is the half width (radian) of the (hkl) plane, and θ is the X-ray reflection angle. It was. The results are shown in Table 6 together with the abundance of (222) oriented crystals.

  Regarding the internal stress in Table 6, a positive value is a tensile stress and a negative value is a compressive stress. According to Table 6, it can be seen that in Examples 1 to 3, the CrMo plating film has compressive residual stress, and the compressive residual stress increases as the amount of catalyst added increases. When the compressive residual stress becomes high, it becomes difficult for oxygen to diffuse from the surface of the plating film to the inside, so that the Cr oxide film formed on the surface of the plating film becomes thin.

  That is, in the case of the example, by adding organic sulfonic acid, as shown in Table 4, the Cr crystal (BCC) atoms are closely packed and the crystal lattice spacing is narrow (222) plane is high, CrMo plating film The compressive residual stress of is high. In addition, when an external force in the direction along the surface is applied to the CrMo plating film by grinding, the Cr crystal lattice is distorted, but since the (222) plane has a narrow crystal lattice spacing, the lattice is deformed. The resulting crystal distortion increases, which further increases the compressive residual stress. Thus, the Cr oxide film is formed by oxygen diffusing from the surface of the Cr plating layer to the inside. However, in the Cr plating layer of the embodiment having a high compressive stress as described above, the crystal lattice spacing is narrowed to reduce the oxygen content. Since the diffusion is difficult to occur, the thickness of the Cr oxide film is reduced.

  According to observation by a transmission electron microscope, in Example 3, the Cr oxide film had a thickness of 6.6 nm, the number of layers was 79, and the surface was smooth. On the other hand, in the comparative example, the Cr oxide film had a thickness of 52.9 nm, the number of layers was 634 layers, and the surface was uneven. The number of layers is determined from the diffraction angle of the (222) plane observed by the X-ray diffraction analysis. Bragg's equation (2 dsin θ = nλ, where d: lattice spacing, θ: diffraction angle, λ; Mo − The crystal lattice plane spacing of 0.0834 nm was obtained from the wavelength of Kα, n = 1), and the thickness of the Cr oxide film was divided by this crystal lattice plane spacing.

  Moreover, the crystallite diameter of (222) orientation of Example 3 and the comparative example is about 15 nm, and in the case of Example 3, the Cr oxide film has a thickness of half or less of the crystallite diameter. On the other hand, in the comparative example, the thickness of the Cr oxide film is several times the crystallite diameter.

  FIG. 3 is a graph showing the relationship between the abundance of (222) oriented crystals and internal stress. As the abundance of (222) oriented crystals in the CrMo plating film increases, the compressive residual stress increases, and when the abundance of the (222) plane exceeds 60%, the compressive residual stress may increase to 20 MPa or more. Recognize.

<Friction and wear characteristics evaluation test>
The friction and wear characteristics of the combinations of various sliding surface materials applied to the sliding surfaces of the two members sliding with each other were evaluated using a pin-on-disk friction and wear tester shown in FIG. In FIG. 4, reference numeral 21 denotes a disk supported on the turntable 22, and 23 denotes pins arranged on the disk 21 at an angular interval of 120 degrees in the circumferential direction of the disk 21.

  A high-speed CrMo plating film or a normal CrMo plating film was formed in an annular shape on the disk 21 so as to go around positions corresponding to the three pins 23. Here, the high-speed CrMo plating film is related to the plating conditions of Example 3 (addition amount of organic sulfonic acid 30 ml / L), and the normal CrMo plating film is the plating conditions of Comparative Example 3 (addition of organic sulfonic acid). Volume 0 ml / L). The pin 23 was formed of silicon nitride, chilled cast iron, zirconia (PSZ), silicon carbide, or carbide (WC-Co).

  The frictional wear test was performed in a lubricated state, the load was 540 N, the peripheral speed of the pin 23 was 1 m / second, the time was 60 minutes, and additive-free turbine oil was used as the lubricating oil.

  FIG. 5 shows the test results of the amount of pin wear. When the pin is formed of silicon nitride, the wear amount of the pin is remarkably smaller than that of chill cast iron or zirconia (PSZ), regardless of whether the disk is plated at high speed CrMo or normal CrMo. Furthermore, the amount of pin wear is smaller in the combination of silicon nitride and high-speed CrMo plating than in the combination of silicon nitride and ordinary CrMo plating.

  FIG. 6 shows a test result of the plating wear amount of the disk. In the combination of silicon nitride and high-speed CrMo plating, the amount of plating wear is as small as each combination of chill cast iron-high-speed CrMo plating, chill cast iron-ordinary CrMo plating, and zirconia (PSZ) -high-speed CrMo plating. Only the combination of ordinary CrMo plating results in an extremely large amount of plating wear.

  In addition, in each combination of silicon carbide-high speed CrMo plating and carbide (WC-Co) -high speed CrMo plating, the wear test was stopped due to scuffing.

  FIG. 7 shows the change over time in the coefficient of friction for various combinations of sliding surface materials. In each combination of chill cast iron-ordinary CrMo plating and chill cast iron-high speed CrMo plating, the friction coefficient becomes a relatively high value within minutes to tens of minutes from the start of the test. In the combination of silicon nitride and ordinary CrMo plating, the friction coefficient is low for a while after the start of the test, but starts to increase after about 20 minutes. On the other hand, in the combination of silicon nitride and high-speed CrMo plating, the test was completed with a relatively low friction coefficient from the start of the test.

  In addition, in the combination of zirconia (PSZ) -high-speed CrMo plating, the friction coefficient is low, but this is a result of a reduction in surface pressure due to a large amount of wear of the pins as can be seen from FIG. Further, in each combination of silicon carbide-high speed CrMo plating and carbide (WC-Co) -high speed CrMo plating, the friction test was stopped due to scuffing.

  As described above, according to the combination of silicon nitride and high-speed CrMo plating, both the pin wear amount and the disk plating wear amount are small, and since it exhibits good low friction characteristics, it is a sliding member for various devices such as engines. When this combination is adopted, it can be seen that high reliability of operation of the device can be obtained even under severe lubrication conditions.

1 Rotor housing (first member)
2 Trochoidal surface (sliding surface)
5 Apex seal (second member)
10 Cr-containing plating film

Claims (4)

  A sliding surface between the first member formed of a plating film containing Cr formed by electrolytic deposition from a plating bath containing a Cr component and an organic sulfonic acid, and the sliding surface between the first member is made of silicon nitride A sliding member comprising a combination of the formed second member. In claim 1,
The plating film is characterized in that the (222) oriented crystal whose (222) plane is directed to the surface side specified by X-ray diffraction analysis has an abundance ratio on the surface of the plating film of 60% or more and 80% or less. A sliding member.   A first member formed by a plating film having a sliding surface containing Cr and having a compressive residual stress of 20 MPa or more is combined with a second member in which the sliding surface with the first member is formed by silicon nitride. A sliding member characterized by comprising: In any one of Claim 1 thru | or 3,
The sliding member, wherein the plating film is made of a CrMo alloy containing Cr as a main component.

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