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- Pettersson, Ulrika, et al.
(författare)
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Friction and wear properties of micro textured DLC coated surfaces in boundary lubricated contacts
- 2004
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Ingår i: Tribology letters. - 1023-8883 .- 1573-2711. ; 17:3, s. 553-559
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, the friction and wear properties of boundary lubricated textured surfaces were investigated. The capability to feed lubricant into the interface of a sliding contact and to isolate wear particles was related to the shape, size and orientation of the texture patterns. Well-defined surface textures of square depressions or parallel grooves of different widths and distributions were produced by lithography and anisotropic etching of silicon wafers. Subsequently the wafers were PVD coated with thin, wear resistant DLC coatings, retaining the substrate texture. The surfaces were evaluated in reciprocating sliding against a ball-bearing-steel ball under starved or amply lubricated boundary lubrication conditions.
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- Pettersson, Ulrika, et al.
(författare)
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Influence of surface texture on boundary lubricated sliding contacts
- 2003
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Ingår i: Tribology International. - 0301-679X .- 1879-2464. ; 36:11, s. 857-864
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Tidskriftsartikel (refereegranskat)abstract
- The friction and wear behaviour of boundary lubricated sliding surfaces is influenced by the surface texture. By introducing controlled depressions and undulations in an otherwise flat surface, the tribological properties can be improved. Lubricant can then be supplied even inside the contact by the small reservoirs, resulting in a reduced friction and a prolonged lifetime of the tribological contact.In the present paper, well-defined surface textures were produced by lithography and anisotropic etching of silicon wafers. The wafers were subsequently PVD coated with thin wear resistant TiN or DLC coatings, retaining the substrate texture. The size and shape of the depressions were varied and evaluated in reciprocating sliding under dry and boundary lubricated conditions.
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- Pettersson, Ulrika, 1975-
(författare)
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Surfaces Designed for High and Low Friction
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis comprises tribological studies of extremely well-defined surfaces of different designs. Both low-friction and high-friction surfaces were manufactured and experimentally evaluated.In the low-friction studies, lithography and anisotropic etching of silicon was first used as a texturing technique. The textured surfaces were subsequently PVD coated with TiN or DLC to achieve tribologically relevant interfaces. The results showed that under starved lubricated conditions, fine surface textures lowered the coefficient of friction and the wear rate. It was shown that also the orientation of the texture is of major importance for the lubricating function.Further, a novel embossing technique was developed, permitting texturing of steel and other materials. A micro mechanically designed diamond tool was used to emboss steel surfaces. The roller/piston contact from a hydraulic motor was simulated and introduction of an embossed texture on the piston decreased the level and the fluctuation of the friction. The effect of the texture was here similar to the effect of an additional polish step. However, in general it is not an easy task to substantially improve a boundary lubricated contact by introducing a texture. Studies of high friction surfaces were performed on micro mechanically designed diamond surfaces equipped with sharp pyramids or ridges. Just as theory predicts, the coefficient of friction was dependent on the shape of the ploughing bodies, but not on the counter material or the load. The tested surfaces resulted in static coefficients of friction between 1.1 and 1.6, depending on surface design and orientation. These are extremely high values, and therefore very interesting for practical applications requiring a high static friction.Conclusively, the present thesis shows that it is possible to design and produce surfaces both for improved lubrication in sliding contact and for substantially improved high friction performance in static contacts.
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- Pettersson, Ulrika, et al.
(författare)
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Textured surfaces for improved lubrication at high pressure and low sliding speed of roller/piston in hydraulic motors
- 2007
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X .- 1879-2464. ; 40:2, s. 355-359
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the potential of surface textures to improve the friction situation of the piston/roller contact in hydraulic motors at low speed and high pressure. A self-adjusting flat on flat rig, with conditions representative of an actual hydraulic motor, is used in a reciprocating sliding motion. The samples are made out of the same materials and the surface finishing operations are the same as used in the motor.The piston surfaces are textured using newly developed embossing tools comprising micromechanically formed all-diamond surfaces. The textured surfaces involve parallel grooves and crossed grooves, each of four different spacings. Also polished surfaces were tested. Un-textured—as tumbled—surfaces are used as reference.Generally, it was found that the friction level was only marginally influenced by the textures. However, the friction fluctuations were reduced. SEM investigations disclosed rather severe modifications of the surfaces during use, primarily caused by plastic deformation of the surface layer. The results and their practical implications are discussed.
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