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| 2. |
- Gerth, Julia, 1979-, et al.
(författare)
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On the wear of PVD-coated HSS hobs in dry gear cutting
- 2009
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 266:3-4, s. 444-452
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Tidskriftsartikel (refereegranskat)abstract
- A hob is an advanced gear cutting tool usually made of homogenous high-speed steel (HSS) and coated by physical vapour deposition (PVD). It is designed for regrinding and recoating many times. However, hobs of today suffer from unpredictable wear making it difficult to schedule when they should be taken out for reconditioning. This investigation is aimed to contribute to the fundamental knowledge of the wear mechanisms and wear propagation of hobs used in dry gear cutting. Two AlCrN-coated hobs, used in actual gear cutting, were investigated by scanning electron microscopy (SEM) to study the tool topography, light optical microscopy (LOM) to study metallographic cross-sections and by X-ray photoelectron spectroscopy (XPS) for surface analyses.It is concluded that the high potential of PVD-coated HSS as tool material is not taken full advantage of. The main reason is a combination of a poor surface preparation prior to coating and excessively high compressive residual stresses, making parts of the coating detach along the edge line even on unused cutting teeth. During cutting, the high intrinsic stresses in combination with droplets and defects in the coating facilitated its fragmentation through decohesion and detachment. Simultaneously, the rake face is gradually covered by a thin oxide layer dominated by Fe, Cr and Mn in about equal amounts, and also with a significant content of Si. It is believed but not proved that this layer is beneficial.To improve service life and reliability of gear cutting hobs, precautions should be taken for the grinding–polishing preparation prior to PVD-coating to ensure a smooth substrate free from burning damage and other defects. Also, the edge radius and coating thickness has to be matched with the magnitude of compressive residual stresses in the coating.
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| 3. |
- Persson, Anders, 1982-, et al.
(författare)
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Ga Implantation in a MgO-based Magnetic Tunnel Junction With Co60Fe20B20 Layers
- 2011
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Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 47:1, s. 151-155
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Tidskriftsartikel (refereegranskat)abstract
- A Co60Fe20B20-based tunneling magnetoresistance multilayer stack with an MgO barrier has been exposed to 30 keV Ga ions at doses corresponding to ion etching and metal deposition in a focused ion beam (FIB) instrument, to study the applicability of these processes to magnetic tunnel junction (MTJ) fabrication. MTJs were fabricated and irradiated to investigate how the exposures affected their coercivity and magnetoresistance. Elemental depth profiles, acquired using electron spectroscopy for chemical analysis, showed that Ga gathered in and around the two Co60Fe20B20 layers. Correlated with the results of the magnetic measurements, this Ga presence was found to cause a reduction of magnetoresistance and an increase in coercivity. Quantitatively, a dose of 1014 Ga+cm-2 reduced the magnetoresistance by 60%, whereas a dose of 1015 Ga+cm-2 reduced the magnetoresistance by 67% and also increased the coercivity by 2 mT and changed the dipole coupling between the sensing and the pinning layers by 1.6 mT. The latter was attributed to an imbalance in the synthetic antiferromagnetic structure, where the stack's Ru spacer served as an implantation barrier. The magnetoresistance was lost at a dose of 1016 Ga+cm-2. Annealing reduced the content of Ga around the magnetic layers but also caused diffusion of Cu from one of the layers in the stack. Apart from the observation and explanation of implantation damages in the multilayer, this work concludes on the applicability of FIB processes for prototyping of MTJs.
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| 4. |
- Persson, Anders, 1982-, et al.
(författare)
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Micro- and nanostructured magnetic field sensor for space applications
- 2009
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Ingår i: 15th International Conference on Solid-State SensorsTransducers 2009. ; , s. 1190-1193
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Konferensbidrag (refereegranskat)abstract
- Magnetometers are popular payloads on scientific space missions. Here, the design and fabrication process of a miniaturized magnetometer based on tunneling magnetoresistance is presented. The process is capable of making magnetic tunnel junctions in a wide size range, by employing both UV lithography and focused ion beam milling and deposition. Ga implantation in the ferromagnetic electrodes of the junction is studied in more detail. It was shown that Ga implantation may harm the magnetometer if the irradiation dose exceeds 1014 Ga+ cm-2.
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| 5. |
- Riddar, Frida, et al.
(författare)
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Comparison of anodised aluminium surfaces from four fabrication methods
- 2012
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 212:11, s. 2272-2281
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Tidskriftsartikel (refereegranskat)abstract
- This study presents a comparative analysis of surface characteristics and properties of anodised aluminium cylinders produced by sand casting, permanent mould casting, extrusion, and high pressure die casting. Differences in micro structure and distribution of silicon particles in the aluminium, due to the fabrication method and the silicon content in the alloy, resulted in varying thickness of the oxide layers (mean thicknesses between 7 and 19 m) and surface topography. The oxide layer was unevenly thick for the permanent mould cast and the sand cast cylinders, resulting in a surface with higher plateaus and lower areas. This was more prominent for the sand cast surface. The oxide of the extruded cylinder was thick and even and its surface was smooth. The high pressure die cast surface had an oxide that was very thin and uneven. The surfaces displayed different results in the scratch test due to the variations in the surface structure. For the permanent mould cast and the sand cast surfaces the silicon particles present in the oxide deflected the cracks that were formed during the scratching. This resulted in smaller wear debris. The nanohardness values of the oxides had a large scattering due to the inhomogeneous nature of the oxide layers, with pores and particles. However, the highest nanohardness values were between 5000 and 6000 MPa for the four surfaces, which is significantly lower than that of sintered alumina. In the micro abrasion test the wear mechanism for all four surfaces was microcutting resulting in chippings.
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| 6. |
- Riddar, Frida, et al.
(författare)
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Comparison of friction performance of four anodised aluminium surfaces for use in a clutch actuator
- 2014
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 319:1-2, s. 227-233
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Tidskriftsartikel (refereegranskat)abstract
- Clutch actuators in the automotive industry are used to convert the force applied by the driver to the clutch. A typical pneumatic actuator consists of an anodised aluminium cylinder in which a piston, with a rubber lip seal and a PTFE guiding ring, slides. The system is silicone grease lubricated. The aluminium cylinder is most often cast, e.g. permanent mould, sand, or high pressure die cast. An interesting alternative is extrusion. After anodising the cylinders display different surface topography due to, amongst other things, the fabrication method. In this study, the friction behaviour of the anodised surfaces from the four mentioned methods are investigated in a reciprocating sliding test. Two test setups were used, one simulating the real contact situation, and one using a simpler sphere on flat geometry. The extruded surface oxide cracked during testing, resulting in very fluctuating friction behaviour. The high pressure die cast surface showed rather good results, but never the best. However, it is considered not suitable for the application due to its poor oxide properties. The permanent mould cast surface displayed the lowest friction coefficient, while the sand cast surface often showed the highest friction.
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| 7. |
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| 8. |
- Riddar, Frida, et al.
(författare)
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Friction, wear and surface damage mechanisms of pneumatic clutch actuators
- 2013
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 305:1-2, s. 36-44
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Tidskriftsartikel (refereegranskat)abstract
- Wear and surface degradation mechanisms of a pneumatic clutch actuator have been studied. The applied test method simulates the sliding contact of an anodised aluminium surface against a rubber lip seal and a PTFE guiding ring. The influences of contact load, temperature and particle contamination on wear mechanisms and friction were investigated. A controlled amount of lubrication was applied; both pure silicone grease and silicone grease mixed with standard dust particles were used.The wear occurring at the tests with only silicone grease is similar, but on a lower scale, to the wear at the tests with a mixture of silicone grease and standard dust. The polishing of the anodised aluminium is increased with increasing temperature or increasing load. The wear of the anodised aluminium surface is more prominent when sliding against the PTFE guiding ring than when sliding against the lip seal. The wear of the guiding ring increases with increasing load or increasing temperature. The lip seal is worn but at 140 °C (with silicone grease or with a mixture of silicone grease and standard dust) or at increased load (with a mixture of silicone grease and standard dust) a thick layer of adhered material is formed.
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| 9. |
- Riddar, Frida, et al.
(författare)
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On the wear of pneumatic clutch actuators
- 2008
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Ingår i: Proceedings of NORDTRIB 2008 : 13th Nordic Symposium on Tribology. - Tammerfors, Finland : Tampere University of Technology.
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Konferensbidrag (refereegranskat)
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| 10. |
- Riddar, Frida, et al.
(författare)
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The effect of lubrication on the friction performance in pneumatic clutch actuators
- 2014
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Ingår i: Wear. - : Elsevier BV. - 0043-1648 .- 1873-2577. ; 309:1-2, s. 166-173
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Tidskriftsartikel (refereegranskat)abstract
- Pneumatic clutch actuators in trucks transform the force applied on the clutch pedal into the force acting on the clutch. The actuator consists of an anodised aluminium cylinder in which a piston, with a rubber lip seal and a PTFE guiding ring mounted on it, slides. The system is lubricated with silicone grease before assembly. Wear of the lip seal will lead to a deteriorated sealing capacity, and ultimately failure.A test setup is used to evaluate the effect of silicone grease amount on friction performance, PTFE transfer and rubber lip seal wear. Reciprocating sliding and vibration tests were performed. The surfaces of cylinders, guiding rings and lip seals were studied by SEM and ESCA.The friction level is highly dependent on the amount of grease in the contact area. During sliding, grease is pushed out from or dragged into the contact area, resulting in a fluctuating friction. Furthermore, even with grease lubrication, PTFE transfer to the aluminium surface occurs. A triple transfer from guiding ring, to aluminium surface, to lip seal, to another part of the aluminium surface was observed. Finally, although the unstable lubricating effect, it was found that the grease protects the lip seal from wear.
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