JP4263185B2 - Low friction sliding surface - Google Patents

Description

The present invention relates to a low-friction sliding surface formed by the fine irregularities in the laser irradiation periodically formed on the solid material surface.

  In recent years, global warming and environmental destruction have become major problems. In particular, reducing friction loss of sliding parts in automobiles and industrial equipment has become an important issue. In view of this, research has been conducted to reduce frictional force and improve seizure resistance by forming fine irregularities such as grooves and dimples on the surface of sliding parts. On the other hand, when the surface of a sliding part is scanned with a linearly polarized femtosecond laser at a fluence near the processing threshold, a grating-like periodic structure having a submicron periodic pitch and amplitude (level difference) can be formed in a self-organized manner. (For example, refer nonpatent literature 1). When this processing method is used, a fine periodic structure can be easily formed even on difficult-to-process materials, and the direction of the periodic structure can be arbitrarily set only by changing the polarization direction. By forming a radial or spiral periodic structure on the sliding surface that rotates continuously, the friction coefficient can be greatly reduced (see, for example, Non-Patent Document 2).

  FIG. 10 is a schematic diagram of the periodic structure creation device. The femtosecond laser 1 is irradiated from the laser generator 31 to the mirror-polished surface of the solid material 2 on the XY-θ stage 35. The laser energy can be adjusted using the half-wave plate 32 and the polarization beam splitter 33, and is condensed by the lens 34 and irradiated onto the surface of the solid material 2.

  FIG. 11 is a schematic perspective view of the periodic structure forming mechanism. In the figure, when a pulse laser of one shot and one pulse is irradiated on the surface of the solid material 2, interference between the p-polarized component of incident light and the p-polarized component of surface scattered light occurs and a standing wave is generated. When the fluence of incident light is near the laser threshold, the interference portion of the p-polarized component of the incident light and the p-polarized component of the scattered light along the surface is ablated. Once ablation begins and the surface roughness increases, the intensity of the surface scattered light increases during the next one-shot laser irradiation, further ablation proceeds, and interference occurs at a position one wavelength λ away. When the incident light is linearly polarized light, repeated laser irradiation causes interference at approximately the same interval as the wavelength λ of the incident light, thereby creating a periodic structure in a self-organized manner. The irregularities of this periodic structure grow to the wavelength order by repeating laser irradiation, but the irregularities become unclear when pulsed laser is irradiated further. Therefore, the periodic structure can be extended to the surface of the solid material 2 over a wide range by controlling the number of shots irradiated at the same position and performing scanning while overlapping the pulse laser.

The periodic structure formed in this manner has a submicron order periodic pitch and an uneven height difference, and greatly contributes to reduction of friction loss of the sliding portion. For example, a periodic structure in which the periodic direction is controlled by the polarization angle is provided on a cemented carbide stationary test piece, and the change in the friction coefficient is examined by a ring-on-disk test. By controlling the periodic direction, tribological characteristics such as the fluid lubrication region, load capacity, and friction coefficient can be adjusted according to the application (for example, see Non-Patent Document 2).
Hiroshi Sawada, Kosuke Kawahara, Takafumi Ninomiya, Hiroshi Kurosawa, Atsushi Yokotani: Formation of fine periodic structure by femtosecond laser, Journal of Precision Engineering, 69, 4, (2003) 554. Hiroshi Sawada, Kosuke Kawahara, Takafumi Ninomiya, Satoshi Mori, Hiroshi Kurosawa: Effect of Femtosecond Laser on the Sliding Characteristics, Journal of Precision Engineering, 70, 1 (2004) 133.

  The periodic structure formed on the sliding part surface has an excellent effect of reducing the friction loss of the sliding part of an automobile or industrial equipment by making the sliding part surface a low friction sliding surface. However, such an effect can be exerted on a continuous sliding surface such as a rotating body that continuously rotates in a fixed direction, but it reciprocates repeatedly moving in a fixed direction, stopping once and then moving in the reverse direction. On the sliding surface, it is difficult to exert the above effect. That is, when the concave and convex periodic structure is formed so as to cross the sliding direction on the entire sliding surface, the gap between the two sliding surfaces becomes small at the portion facing the convex and concave portions, so-called wedges. Since the load capacity due to the effect is generated and the oil film is formed, the friction loss of the sliding surface can be reduced. However, when the sliding surface is a reciprocating sliding surface, the concave / convex recess has a groove structure with openings at both ends, and therefore, side leakage occurs such that the oil film flows out from the opening end of the recess once the sliding stops. However, the oil film holding capacity on the periodic structure is reduced, the oil film is reduced, and the friction loss of the sliding portion at the time of restart is increased. This is evident from the following specific reciprocating sliding test.

FIG. 12A shows a mirror-side stationary test piece 3a that does not form a periodic structure. FIG. 13 (A) shows a stationary side test piece 3b in which the periodic structure 4 is formed by a full pattern. Each stationary side test piece 3a, 3b was made of cemented carbide having a diameter of 20 mm (chamfered in a sliding direction with a width of 18 mm), and the surface before forming the periodic structure was set to Ra 0.05 μm or less. A drive side test piece (not shown) was made of a cemented carbide of 50 mm × 30 mm, and the sliding surface roughness was Ra 0.05 μm or less. The load at the time of the sliding test is 30 N, 75 mg of turbine oil (VG32) is supplied to the sliding surface, the sliding coefficient is steady at a sliding length of 10 mm, a sliding speed of 1 mm / s, and a sliding end stop time of 1 s. Familiar operation was carried out until it became, and after 24 hours of stoppage, the change in the friction coefficient when restarted under the above conditions was investigated.

  FIG. 12B shows the change of the friction coefficient at the first reciprocation after the restart in the mirror surface test piece 3a not forming the periodic structure together with the steady state value. The mirror-surface test piece 3a shows a constant coefficient of friction regardless of the sliding time in the steady state, and the oil film is hardly affected by the 1s stoppage at the sliding end. However, the response of the reduction of the friction coefficient immediately after the restart is poor, the friction coefficient after the sliding 2s (sliding distance 2mm) is 60% of the maximum friction coefficient, and the friction after the sliding 8s (sliding distance 8mm) The trend of decreasing coefficient disappears. Ten or more reciprocations are required until the friction coefficient reaches 0.01. In such a mirror-shaped test piece 3a, only the unintended waviness or elastic deformation of the test piece contributes to the formation of the oil film, and therefore, it is considered that the response of reducing the friction coefficient is poor.

  FIG. 13B shows the change of the friction coefficient at the first reciprocation after the restart in the test piece 3b in which the periodic structure 4 is formed in the entire pattern, together with the steady state value. Even in a steady state, the entire surface pattern does not show a constant coefficient of friction like the mirror-finished test piece 3a, but shows a high coefficient of friction immediately after the drive is applied, and the coefficient of friction decreases as the sliding time increases. The entire surface pattern has a load capacity due to the wedge effect at the time of sliding, and an oil film is formed. However, since the recesses (grooves) in the irregularities of the periodic structure 4 are opened to the side surface, the oil film holding ability at the time of stopping is lowered When a 1 s dwell time is sandwiched, an oil film is cut and a high coefficient of friction is exhibited even after 10 reciprocations. Such a periodic structure 4 having an overall pattern exhibits excellent characteristics in a rotating body that continuously slides, but becomes a fatal defect in reciprocating sliding. Moreover, since side leakage occurs, the response of reducing the friction coefficient during sliding is poor.

  An object of the present invention is to provide a sliding surface structure that is also excellent in reciprocating sliding characteristics with stopping.

In order to achieve the above object, the present invention achieves the above object by dividing any region of the plurality of discrete regions of the mirror surface portion forming the solid material surface by being surrounded by the mirror surface portion, and the mirror surface portion is a continuous surface. A grating-like periodic structure is formed in the plurality of regions .

  Here, the surface of the solid material is a mirror surface of a cemented carbide or the like, and is referred to as a mirror surface portion so as to be distinguished from a plurality of discrete regions where a periodic structure is formed. Each of the plurality of discrete regions in which the periodic structure is formed is divided by a mirror surface portion. The term “discrete” means that all of the plurality of regions are separated from each other via the mirror surface portion and dispersed. The shape, area, and direction of the periodic structure in each of the plurality of regions in which the periodic structure is formed are variously set according to the shape, area, and application of the sliding surface. Since any of the plurality of regions is divided by the mirror surface portion, the end of the grating-shaped concave / convex concave portion (groove) of the periodic structure formed in the region is located at the boundary portion with the mirror surface portion, and the opening of the groove end Becomes a state of being dammed by the mirror surface portion, side leakage of the oil film is suppressed, and the oil film holding ability is maintained high.

  In the present invention, each of the plurality of regions has substantially the same shape and substantially the same area, and a periodic structure can be formed on the entire surface of each region. Here, “substantially the same” means that they are the same when viewed macroscopically, but there are minute differences within an allowable range when viewed microscopically. A rectangular shape, a sector shape, a circular shape, or the like can be selected as the shape of each of the plurality of regions dispersed in a discrete pattern. By making the shape and area of the plurality of regions substantially the same, it is easy to form a periodic structure in each region, and the sliding characteristics of the entire sliding surface can be made uniform.

  In the present invention, the periodic structures formed in the plurality of regions can be aligned in a direction substantially parallel to the sliding direction. The direction of the periodic structure is a convex portion direction or a concave portion direction orthogonal to the grating-like uneven direction, and the periodic structure is formed so that this direction is parallel to the sliding direction. If it does in this way, the oil film side leakage from the recessed part edge of a periodic structure can be controlled more reliably, and it will become what was excellent in oil film retention capability.

  In the present invention, the amplitude of the grating-like irregularities of the periodic structure and the depth of the concave portions of the grating-like irregularities from the mirror surface portion are substantially the same, and the height of the maximum convex portions of the grating-like irregularities is the mirror surface portion. Keep the level below the level. Furthermore, in the present invention, the amplitude of the grating-like irregularities of the periodic structure is set to 1 μm or less. Further, the periodic pitch of the grating-like irregularities of the periodic structure is made 10 μm or less.

  By implementing any dimensional regulation of such grating-like irregularities, or by implementing all dimensional restrictions, the sliding performance by the cooperation of the periodic structure and the mirror surface portion on the sliding surface can be improved. , Can be more stable.

Further, in a method of forming a grating-like periodic structure into discrete plurality of regions of the mirror portion forming a solid material surface is irradiated with laser linearly polarized light fluence of processing threshold near the solid material surface, irradiated portion thereof the scans while overlapping to form a self-organizing manner periodic structure, that form a periodic structure having a uniform direction only discrete plurality of regions so as to intermittently perform laser irradiation.

  The intermittent laser irradiation here is performed, for example, by on / off control of laser oscillation from the laser generator, or by light shielding control by a light shielding plate arranged in the optical path of the laser oscillated from the laser generator. it can. In this way, by periodically performing laser irradiation to form a periodic structure only in a plurality of discrete regions, it is easy to form a periodic structure having a uniform direction in each region.

  According to the present invention, since each of the plurality of periodic structures discretely formed on the sliding surface is divided by the mirror surface portion, both ends of the concave portions of the grating-like irregularities of each periodic structure are blocked by the mirror surface portion. As a result, the oil film holding capacity in each periodic structure is increased, the response of the decrease in the coefficient of friction after sliding is improved, and the reciprocating sliding characteristics and rotational sliding characteristics can be further improved. In particular, by making the periodic structure parallel to the sliding direction, the sliding characteristics can be stabilized and further improved.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. Moreover, the sliding test result of the sliding surface in various embodiment is demonstrated with reference to FIGS.

  A circular sliding surface 10a shown in FIG. 1 (A) includes a mirror surface portion 11a having a lattice pattern and a periodic structure 13a formed in a plurality of discrete rectangular regions 12a surrounded by the mirror surface portion 11a. Is done. One rectangular region 12a is, for example, a rectangle of 0.3 mm × 1.0 mm, and the periodic structure 13a is formed on the entire surface in a direction parallel to the sliding direction X of the sliding surface 10a. Adjacent periodic structures 13a are partitioned by a mirror surface portion 11a having a width of 0.3 mm, for example. The mirror surface portion 11a is one surface that is continuous in a vertical and horizontal grid pattern. The width and pattern of the mirror surface portion 11a and the region size and shape of the periodic structure 13a are not particularly limited. The entire sliding surface 10a before forming the periodic structure 13a is a flat mirror surface, and a plurality of discrete rectangular regions 12a on the mirror surface are irradiated with linearly polarized laser at a fluence near the processing threshold, The periodic structure 13a is formed in a self-organized manner by scanning while overlapping. The periodic structure 13a may be formed using the apparatus shown in FIG. In this case, for example, by performing on / off control of laser oscillation from the laser generator 31 of FIG. 10, the periodic structure 13a is formed in the same direction only in the plurality of discrete rectangular regions 12a. Hereinafter, the sliding surface 10a of FIG. 1 is referred to as a parallel intermittent sliding surface 10a as necessary to distinguish it from other embodiments.

  FIG. 1B is a partially enlarged sectional view of the mirror surface portion 11a and the periodic structure 13a. The periodic structure 13a has a convex portion 14 and a concave portion 15 that form grating-like irregularities. The average amplitude h of the grating-like irregularities is set so as not to exceed 1 μm, and the depth i from the mirror surface portion 11a of the concave portion 15 and the amplitude h are substantially the same. Further, the height of the largest convex portion 14 of the grating-like unevenness is set to be equal to or less than the height of the mirror surface portion 11a, and the apex of the convex portion 14 is at a position lower than the mirror surface portion 11a and protrudes above the mirror surface portion 11a. I'm not going to do that. Furthermore, the periodic pitch p of the grating-like irregularities of the periodic structure 13a is set to a size not exceeding 10 μm. The reason for such dimensional regulation will be described in the sliding test described later. It should be noted that the above-described dimensional restrictions are similarly applied to the other embodiments of FIGS.

  A circular sliding surface 10b shown in FIG. 2 includes a mirror surface portion 11b having a lattice pattern and a periodic structure 13b formed in a plurality of discrete rectangular regions 12b surrounded by the mirror surface portion 11b. One rectangular region 12b is a rectangle of 0.3 mm × 1.0 mm, and the periodic structure 13b is formed on the entire surface in a direction orthogonal to the sliding direction X of the sliding surface 10b. Adjacent periodic structures 13b are partitioned by a mirror surface portion 11b having a width of 0.3 mm. The sliding surface 10b shown in FIG. 2 corresponds to the sliding surface 10a shown in FIG. 1 rotated by 90 °. Hereinafter, the sliding surface 10b shown in FIG. Called.

  The circular sliding surface 10c shown in FIG. 3 is a periodic structure 13c formed in a plurality of discrete regions 12c of a striped pattern formed between a mirror surface portion 11c of a striped pattern and an adjacent mirror surface portion 11c. Composed. The width of the mirror surface portion 11c is about 1 mm, and the width of the striped region 12c is about 1 mm. The periodic structure 13c is formed on the entire surface in a direction orthogonal to the sliding direction X of the sliding surface 10c. Hereinafter, the sliding surface 10c of FIG. 3 is referred to as an orthogonal striped sliding surface 10c as necessary.

Each embodiment of the above FIGS. 1-2 is suitable for the reciprocating sliding accompanied by a stop. The circular sliding surface 10d of the embodiment shown in FIG. 4 is suitable for rotational sliding. The sliding surface 10d of FIG. 4 has a circular ring shape, and a periodic structure 13d having grating-like irregularities is formed in a plurality of regions 12d that are discrete in a ring shape. The region 12d is a fan-shaped rectangular region of 0.3 mm × 0.4 mm, and a mirror surface portion 11d having a width of 0.1 mm exists around the region 12d. The sliding direction X ′ of the sliding surface 10d is a circumferential direction centered on the center of the sliding surface 10d, and the direction of each periodic structure 13d is aligned with the sliding direction X ′.

Next, the reciprocating sliding test of each embodiment of FIGS. 1-2 will be described in order, and finally the rotating sliding test according to the embodiment of FIG. 4 will be described. As in the tests described in FIGS. 12 and 13, the reciprocating sliding test is performed with a load of 30 N, 75 mg of turbine oil (VG32) supplied to the sliding surface, a sliding length of 10 mm, and a sliding speed of 1 mm / s, familiar operation was performed until the friction coefficient reached a steady state at the sliding end stop time of 1 s, and after 24 hours of stoppage, the change of the friction coefficient when restarted under the above conditions was examined.

・ [Reciprocating sliding test of parallel intermittent sliding surface 10a]
FIG. 5 shows the change in the friction coefficient at the first reciprocation after the restart in the test piece having the sliding surface 10a in which the periodic structure 13a is formed in the parallel intermittent pattern, together with the steady state value. In the parallel intermittent pattern, since the end of the concave portion 15 of the periodic structure 13a is dammed by the mirror surface portion 11a, the oil film is hardly cut even when the sliding end is stopped, unlike the entire surface pattern. Therefore, the oil film was hardly affected by the 1 s stop at the sliding end, and showed a constant coefficient of friction regardless of the sliding time in the steady state, as in the case of the mirror specimen. Further, during sliding, the lubricating oil flowing along the concave portion 15 of the periodic structure is blocked by the mirror surface portion 11a, and a large pressure is generated at the boundary portion between the concave portion 15 and the mirror surface portion 11a, so the periodic structure parallel to the sliding direction. However, load capacity arises. Furthermore, since it is partitioned by the protrusions 14 at submicron intervals in the width direction, side leakage hardly occurs and load capacity is efficiently generated, so the response of the friction coefficient after restart is extremely fast, The coefficient of friction after the sliding 2s (sliding distance 2 mm) is reduced to 0.02 or less, and the coefficient of friction after the sliding 6s (sliding distance 6 mm) is almost the same as in the steady state. The friction coefficient at the beginning of the second and subsequent sliding is as low as 0.01, and the friction coefficient change that does not change from the steady state is shown at the tenth time. The convex part 14 of the periodic structure 13a does not protrude with respect to the mirror surface part 11a, and the oil film is extremely thin when restarting after stopping by forming the periodic structure 13a in a section completely partitioned by the mirror surface part 11a. In some cases, the entire section in which the periodic structure 13a is formed acts as an oil reservoir, and has a function of generating load capacity immediately after startup.

  Further, at the time of starting and stopping, the sliding counterpart side is slid by the mirror surface portion 11a, and only an oil film is interposed between the periodic structure 13a and the counterpart side. Wear is suppressed as much as possible. If the convex part 14 of the periodic structure 13a protrudes from the mirror surface part 11a even a little, the protruding convex part comes into contact with the sliding counterpart side to reduce the oil film holding ability, and wear between both tends to occur. Moreover, the thickness of the oil film formed at the time of sliding is determined according to the unevenness of the periodic structure 13a. As the oil film becomes thicker, the rigidity decreases, and the oil film thickness fluctuation at the time of stopping and starting increases, resulting in a decrease in sliding accuracy. Therefore, the average amplitude h of the grating-like irregularities is set to a value not exceeding 1 μm. Further, in order to reduce the side leakage as much as possible, it is desirable that the periodic pitch p is small, and the periodic pitch p is set not to exceed 10 μm so as not to be affected by unintended undulation of the sliding material. If the depth i of the concave portion 15 from the mirror surface portion 11a is increased to twice or three times the amplitude h and the periodic structure 13a is formed deep from the mirror surface portion 11a, the amount of oil film that can be retained increases. Since the effect of preventing side leakage by the periodic structure 13a is lowered during the movement, the depth i of the concave portion 15 from the mirror surface portion 11a is set to be in the range of 1 to 2 times the amplitude h.

・ [Reciprocal sliding test of orthogonal intermittent sliding surface 10b]
FIG. 6 shows the change of the friction coefficient at the first reciprocation after the restart on the sliding surface 10b on which the orthogonal intermittent pattern is formed, together with the steady state value. In the orthogonal intermittent pattern, the side leakage is greatly reduced as compared with the entire surface pattern because it is partitioned by the mirror surface portion 11b every 0.3 mm in the width direction, and the response of the reduction of the friction coefficient after the restart is next to the parallel intermittent pattern. The friction coefficient after sliding 2s (sliding distance 2 mm) was reduced to 1/3 of the maximum friction coefficient, and the friction coefficient decreased to 0.01 near the sliding end. In this case as well, the friction coefficient change that does not change from the steady state is shown at the 10th time.

・ [Reciprocating sliding test of orthogonal stripe sliding surface 10c]
FIG. 7 shows the change in the friction coefficient at the first reciprocation after the restart on the sliding surface 10c on which the striped pattern is formed, together with the steady state value. In the striped pattern, since the side leakage is reduced by the mirror surface portion 11c remaining every 1 mm, the oil film breakage does not occur in the stationary state at the sliding end for 1 s. A constant coefficient of friction was exhibited regardless of time. In addition, since the load capacity due to the periodic structure 13c also occurs during sliding, the friction coefficient after restart decreases with the sliding time, the friction coefficient decreases to 0.015 near the sliding end, and the friction coefficient is steady at the 10th reciprocation. It becomes almost the same as the state. In the case of a striped pattern, the responsiveness of reducing the friction coefficient is not as high as that of the parallel intermittent pattern or the orthogonal intermittent pattern, but there is an advantage that it can be easily formed.

[Fig. 4 Rotating sliding test of sliding surface 10d]
The present invention is effective not only for reciprocal sliding but also for rotational sliding. In the rotational sliding test of the sliding surface 10d shown in FIG. 4, a ring-on-disk sliding is performed on a ring-shaped sliding surface 10d having a mirror surface and a grating-like periodic structure formed discretely and having an outer diameter of 16 mm. Performed in the test. In the sliding surface 10d, the periodic structure 13d is disposed in a rectangular area of 0.3 mm × 0.4 mm, and a mirror surface portion 11d of 0.1 mm remains around the rectangular area. The load was constant at 10N, and the sliding speed was decelerated step by step from 1.2m / s to 0.15m / s in pure water every minute. The change pattern of the sliding speed at this time is shown in FIG.

  In the sliding surface 10d in which the periodic structure 13d is discretely formed, a phenomenon characteristic to the fluid lubrication region in which the friction coefficient decreases as the sliding speed decreases as shown in FIG. / s to 0.15 m / s). In an experiment using a specular test piece, as shown in FIG. 9B, the friction coefficient increases as the speed decreases. Further, when the periodic structure is formed on the entire surface without being discrete, even the radial periodic structure showing fluid lubrication in the widest range is mixed lubrication at less than 0.35 m / s (see Non-Patent Document 2). It was confirmed that the sliding characteristics can be improved by discretely forming the periodic structure 13d as in the sliding surface 10d.

(A) is a top view including the partial enlarged view which shows embodiment of the low friction sliding surface which concerns on this invention, (B) is the partial expanded sectional view of a sliding surface. It is a top view including the elements on larger scale showing other embodiments of a low friction sliding surface. It is a top view including the partial enlarged view which shows the reference example of a low friction sliding surface. It is a top view including the elements on larger scale showing other embodiments of a low friction sliding surface. 1 is a graph of the friction coefficient / sliding time for explaining the reciprocating sliding test of the sliding surface. 2 is a graph of friction coefficient / sliding time for explaining the reciprocating sliding test of the sliding surface. 3 is a graph of friction coefficient / sliding time for explaining the reciprocating sliding test of the sliding surface. 4 is a speed change pattern diagram for explaining the rotational sliding test of the sliding surface. (A) is a graph of the friction coefficient / sliding time for explaining the rotational sliding test of the sliding surface in FIG. 4, and (B) is a graph of the friction coefficient / sliding time on the mirror surface. It is a schematic diagram of a periodic structure creation apparatus. It is a schematic perspective view for demonstrating the principle of a periodic structure formation mechanism. (A) is a plan view of the sliding surface of the mirror surface, and (B) is a graph of friction coefficient / sliding time for explaining the reciprocating sliding test of the sliding surface. (A) is a plan view of a sliding surface having a periodic structure on the entire surface, and (B) is a graph of friction coefficient / sliding time for explaining a reciprocating sliding test of the sliding surface.

Explanation of symbols

2 Solid materials 10a to 10d Low friction sliding surfaces 11a to 11d Mirror surface portions 12a to 12d Discrete regions 13a to 13d Periodic structure 14 Convex part 15 Concave part 31 Laser generator 32 Wave plate 33 Polarizing beam splitter 34 Lens

Claims (6)

All regions of the plurality of discrete regions of the mirror surface portion forming the solid material surface are divided by being surrounded by the mirror surface portion, and the mirror surface portion is a continuous surface . A low-friction sliding surface characterized by forming a periodic structure.   The low friction sliding surface according to claim 1, wherein each of the plurality of regions has substantially the same shape and substantially the same area, and a periodic structure is formed on the entire surface of the region.   The low friction sliding surface according to claim 1, wherein the periodic structure is formed in a direction substantially parallel to the sliding direction.   The amplitude of the grating-like irregularities of the periodic structure is substantially the same as the depth of the concave portions of the grating-like irregularities from the mirror surface portion, and the height of the largest convex portion of the grating-like irregularities is a height that is flush with the mirror surface portion. The low friction sliding surface according to any one of claims 1 to 3, wherein the sliding surface is low.   The low friction sliding surface according to any one of claims 1 to 4, wherein the amplitude of the grating-like irregularities of the periodic structure is 1 µm or less.   The low friction sliding surface according to any one of claims 1 to 5, wherein the periodic pitch of the grating-like irregularities of the periodic structure is 10 µm or less.

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