| 1. |
- Gåhlin, Rickard, et al.
(författare)
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Wear volume and wear distribution of hydraulic motor cam rollers studied by a novel atomic force microscope technique
- 1998
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Ingår i: Wear. - 0043-1648 .- 1873-2577. ; 220:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The wear volume and wear distribution of chromium steel cam rollers in a high-torque hydraulic motor has been investigated. The cam roller is a part of a novel silicon nitride/chromium steel journal bearing system. An atomic force microscope (AFM) was used to obtain topographical images of the cam roller surfaces before and after use in a full-scale test of the hydraulic motor. The surfaces were marked with small Vickers indentations to make it possible to reposition the AFM to the same locations. To measure the microscopical wear and produce high resolution maps of the local distribution of wear, a recently developed method was utilised. The method is based on two techniques to treat digital topographical images. To map the distribution of wear, the image of the unworn surface is substracted by the image of the worn surface. To measure the wear volume, the bearing histogram is used to calculate a volume relative to a fixed depth. The calculated volume of the unworn surface is then subtracted by the volume of the worn surface. The ceramic/metal system displayed an extremely low wear rate. corresponding to a typical total mean wear depth of about 30 nm. The surface topography showed very limited changes with the minute wear mainly localised to the uppermost part of the surface ridges. The adopted method thus allowed a unique high resolution mapping and volumetric measurement of the initial stages of wear (1 mg lost out of 600 g) on a real machine element. This high resolution analysis is promising for improving tribological testing of real machine elements with long expected wear lives, by reducing the need for excessively accelerated tests or extremely long and costly test durations.
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| 2. |
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| 3. |
- Isaksson, Ove, et al.
(författare)
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Performance improvement under boundary lubrication conditions using slider bearings with silicon nitride/steel in high torque hydraulic motors
- 2000
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Ingår i: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 122:1, s. 348-353
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Tidskriftsartikel (refereegranskat)abstract
- The influence of materials and surface topography on static and dynamic coefficients of friction was experimentally investigated in a test apparatus under boundary and mixed lubrication conditions. Specimen materials were gray iron and silicon nitride (Si3N4) of different surface topographies, sliding against chromium steel at a maximum Hertzian line contact pressure of 50 MPa. The lubricant was a standard mineral-based hydraulic fluid (ISO VG 68) held at +40°C or -28°C. The static and dynamic coefficients of friction under boundary lubrication conditions were both significantly reduced by the change from grey iron to silicon nitride as sliding material against Cr-steel, while the lowest static friction with Si3N4 was found for an intermediate surface roughness.
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| 4. |
- Larker, Rickard, et al.
(författare)
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AEM investigation of ceramic/incology 909 diffusional reactions after joining by HIP
- 1994
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 29:16, s. 4404-4414
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion bonding by hot isostatic pressing (HIP) was performed between Incoloy 909 and five different ceramics. Two of the ceramics were composites made from powder mixtures of Si3N4 and either 60 vol% TiN or 50 vol% TiB2, while three were monolithic materials, namely Si3N4 with 2.5 wt% Y2O3 as a sintering additive, Si3N4 without additives, and Si2 N2O without additives. A diffusion couple geometry was developed to facilitate the preparation of thin-foil specimens for examination by analytical electron microscopy (AEM). Diffusion bonding was performed by HIP at 927°C (1200K) and 200 MPa for 4 h. The formation of reaction layers was very limited, being less than 1 μm in total layer thickness. Two reaction products were found by AEM; a continuous, very thin, (≤100 nm) layer of fine TiN crystals at the initial ceramic/metal interface, and larger grains extending about 100–500 nm into the superalloy and forming a semi-continuous layer of a G-phase suicide containing mainly nickel, silicon and niobium.
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| 5. |
- Larker, Rickard, et al.
(författare)
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Diffusion bonding of CMSX-4 to UDIMET 720 using PVD-coated interfaces and HIP
- 1999
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Ingår i: Journal of engineering for gas turbines and power. - : ASME International. - 0742-4795 .- 1528-8919. ; 121:3, s. 489-493
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Tidskriftsartikel (refereegranskat)abstract
- There is an increasing interest in development of manufacturing methods for Dual Property BLISKs, consisting of creep resistant airfoils and fatigue resistant disks bonded together by a durable joint. Optimum heat treatments are, however, very different for creep resistant single crystal CMSX-4 and fatigue resistant polycrystalline Udimet 720 selected in this study, but fortunately the first aging treatment for CMSX-4 (1140°C, 2-6 h, AC) is similar to the partial solution treatment of U 720 HS2 (1115°C, 4 h, OQ). Based on this, diffusion bonding was performed by HIP at 1120°C and 200 MPa argon pressure for 4 h, followed by cooling to 400°C. Subsequently, a shortened Udimet 720 HS2 two-step aging treatment was adopted by heating to 650°C for 6 h followed by cooling to 400°C, heating to 760°C for 2 h, and finally cooling to R.T. under remaining HIP pressure. Plasma etching followed by thin (80 nm) PVD coating with either nickel or titanium were used to clean and protect the polished surfaces before joining. The selection of coatings was governed by the possibility to reduce oxidized nickel by flushing with hydrogen at 330°C during evacuation of the HIP capsules, and by the large solubility of oxygen in titanium. Hot tensile testing was performed at 750°C on both joined and reference materials subjected to the modified heat treatment. Initially solution treated Udimet 720 and CMSX-4 comprised the reference materials. The testing showed that joints with Ni-PVD coatings were almost as strong as Udimet 720 (although with very limited elongation), while the joints with Ti-PVD coatings were weaker.
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| 6. |
- Lindholm, Per, 1971-
(författare)
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Wear resistant low friction coatings for engine components
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Engine development today is driven by cost, performance and government regulations. Customers want cars and trucks to consume less fuel, last longer, pollute less and be safer. Several of the requirements have tribological associations. For example, product longevity can be improved by lowering friction and using more wear-resistant components. In recent decades, the use of new coating application procedures and techniques has produced remarkably advances in relation to cutting tools. The process temperature at which coatings are applied has been lowered to below 200 oC. Thus it is now possible to coat low-alloy temper-sensitive steels, which are widely used in the automotive industry in machine elements such as gears, bearings and cam followers. The aim of this work has been to investigate the possibility of using sputtered amorphous carbon coatings to reduce friction and prevent wear in engine components, and specifically in valve train components. Test equipment simulating near-normal running conditions for the valve mechanism has been developed and used to test standard and coated valve components. The mechanism has also been analysed and simulated numerically. The results show a low velocity difference between the injector cam lobe and the roller, except for a short interval at the top dead centre of the rocker arm. In that region the slip increases significantly at higher speeds due to inertial forces. A three-dimensional finite element parameter study of the coating thickness, elastic modulus, asperity contact size and wavelength has shown that tensional stresses at the coating surface increase significantly when asperity contacts approach and interact. Testing of different thicknesses in rolling contact, together with finite element stress analysis, showed that a higher tensional stress level through the coating thickness increases the possibility of cracks propagating down to the interlayer and causing delamination of the coating. Tests with a rapid load increase on two carbon coatings show no transition from mild to more severe wear. Instead the contact is dimensioned by the plastic deformation of the underlying substrate.
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| 7. |
- Persson, Jeanette, et al.
(författare)
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Oxidation Studies of Si2N2O
- 1991
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Ingår i: Proc. 4th Internat. Symp. Ceramic Materials and Components for Engines. - London & New York : Elsevier Applied Science. ; , s. 1187-1194
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Konferensbidrag (refereegranskat)
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