Ultrasonic motors typically have a friction drive system to transfer the movement. The miniaturized motor type investigated here has a friction drive system consisting of two drive pads that transfer ...the high frequency oscillating movement of two piezoelectric elements to a linear drive rail. The pads and rail consist of alumina.
Fiction tests were carried out to investigate how the coefficient of friction between the drive pads and the drive rail depends on the number of strokes of the rail. It was found to initially increase with the number of strokes and then stabilize.
Scanning electron microscopy studies of the friction drive surfaces show how a tribofilm forms and develops with the number of strokes. Interestingly, the smooth tribofilm surface gives a higher coefficient of friction than the original rougher surface. To further investigate the nature of the tribofilm, cross section samples were produced with a focused ion beam instrument. The tribofilms show different characters and appear to form gradually by agglomeration and sintering of wear debris. Transmission electron microscopy showed the tribofilm to be amorphous and partly nano-crystalline. This high resolution investigation also clearly demonstrated that the tribofilm bonds very well to the underlying alumina grains.
The processes of friction increase and tribofilm build-up stabilize early compared to the lifetime of the motor.
This work aims to study and understand the influence of the surface topography on wear of grey cast iron used for heavy duty diesel engine cylinder liners. A micro-alloyed grey cast iron was tested ...with different surface topographies. These were polished surfaces, honed surfaces (with two different honing parameters) and three model surfaces with well defined grooves on a polished specimen.
Reciprocating friction tests using a steel ball rubbing against a flat or a cylindrical sample (extracted from a cylinder liner) were carried out on a Cameron Plint test rig. A commercial synthetic oil for diesel engine was used as the lubricant. The friction coefficient and the electrical contact resistance were measured during the tests. The wear volume of the cylinder liner part was also measured at the end of the test.
The influence of the surface topography on the tribochemical film formation and on the wear behaviour of cast iron was established. Surfaces exhibiting lots of surface asperities had the highest wear, mainly due to delayed formation of protective tribochemical film. In our test conditions, the spacing between the grooves on model specimens had no influence on the wear behaviour of the cast iron specimens.
The layered M
n+1
AC
n
ternary carbides – MAX phases – Ta
2AlC, Ti
2AlC, Cr
2AlC and Ti
3SiC
2 were tested under dry sliding conditions against alumina at 550
°C and 3
N load (for a stress of ≈0.08
...MPa) using a pin-on-disk tribometer. Ta
2AlC and Ti
2AlC exhibited low specific wear rates, SWRs, (≤1
×
10
−6
mm
3/N
m), while the coefficients of friction,
μ, were ∼0.9 and ∼0.6, respectively. At 0.4,
μ of Ti
3SiC
2 was the lowest measured, but the SWR, at ≈2
×
10
−4
mm
3/N
m, was high. With a
μ of 0.44 and a SWR of 6
×
10
−5
mm
3/N
m the Cr
2AlC sample was in between. No visible wear of Al
2O
3 counterparts was observed in all the tribocouples. Tribofilms, which were mainly comprised of X-ray amorphous oxides of the M and A elements and, in some cases, unoxidized grains of the corresponding MAX phases, were formed on the contact surfaces. The correlations between observed tribological properties and tribofilm characteristics are discussed.
Contact lenses have a special effect on the treatment of some eye diseases. The tribological behaviour of soft contact lenses considerably influences their clinical performance. Improper wearing of ...contact lenses can lead to mechanical damage of the contact interface, which can lead to pathological changes in the eyeball. In this study, the sliding friction of two kinds of typical contact lens materials (hilaficon-B and lotrafilcon-B) in three lubricants (distilled water, care solution, and eye drop) and tribological parameters are studied, using PMMA as a control. Hydrogels have high water content but the dehydration rate is high. Silicone hydrogels have low initial water content but low dehydration rates. The friction test in distilled water gives the highest coefficient of friction value. The care solution and eye drop significantly reduce the friction coefficient of the lens due to the formation of tribofilm.
Three Al2O3-based suspensions were prepared using two nano-sized Al2O3 powders of analogous size distribution and chemical composition but different agglomeration behaviour, and a micron-sized Al2O3 ...powder. High velocity suspension flame sprayed (HVSFS) coatings were produced using these suspensions as feedstock and adopting two different sets of deposition parameters. Ball-on-disc testing showed that the coatings produced by the micrometric powder suspension were denser and more wear resistant than those deposited using the two nanopowder suspensions, irrespective of the deposition parameters. The tribological behaviour of all coatings was dictated by the formation and subsequent removal of surface tribofilms: these tribofilms were more stable in the coatings obtained by the micrometric powder suspension. However, XRD and hole drilling tests revealed that these coatings exhibited the largest tensile residual stress. Although the coatings were relatively smooth (Ra about 1.3-2 micron), polishing to Ra about 0.1 micron further improved the wear resistance in all cases, as it delayed the onset of tribofilm delamination phenomena.
Zinc dialkyldithiophosphate (ZDDP) film thickness measurements made using in situ ultrathin-film interferometry and described in Part I of this two-part paper (Fujita, et al.
1
), have been used to ...develop and test kinetic models of antiwear film formation and removal. The main component of ZDDP film formation involves the gradual coverage of the surfaces by thick, discrete islands of film material. This process can be modeled by combining a simple coverage model in which the rate of film formation is proportional to the fraction of surface not yet covered, with an induction period. The process of film removal can be modeled by assuming that the rate of film loss is proportional to the fourth power of the coverage or film thickness. The combination of these film formation and removal rate equations is able to predict the complex, transient maximum film-forming behavior of secondary ZDDP as well as the process of film formation by primary ZDDP and the removal of antiwear film by dispersant additive.
Presented at the STLE Annual Meeting in Toronto, Ontario, Canada May 17-20, 2004
Review led by Elaine Yamaguchi
Owing to the requirements of the stable operation for mechanical components, the urgent challenges are to control tribological moisture sensitivity of protective coatings. In this letter, a-C:Si and ...a-C:Si:Al carbon-based coatings were successfully fabricated via magnetron sputtering Si, Al, and C. The microstructure, mechanical properties, and tribological moisture sensitivity of as-fabricated carbon-based coatings were comparatively investigated. Results showed that the as-fabricated a-C:Si and a-C:Si:Al coatings were dominated by typical amorphous structure. The co-introduction of Al could effectively relax internal stress and improve adhesive strength as well as maintain the moderately high hardness for the as-fabricated coating. The striking improvement in tribological moisture sensitivity of a-C:Si:Al carbon-based coating was mainly attributed to the superior mechanical properties and the formation of continuously compacted graphitized tribofilm under low relative humidity condition as well as low shear strength colloidal silica tribofilm under high relative humidity condition. The good balance between the hardness and toughness, low internal stress, and superior low tribological moisture sensitivity of a-C:Si:Al coating make it a good candidate for solid lubricating coating in engineering applications.
An iron oxide layer (mixture of Fe
3O
4 and FeO) was formed by water-vapor treatment on tool steel plates. Bearing steel cylinders were slid against the plates in PAO with and without 1% zinc ...dialkyldithiophosphate (ZDDP) at 80
°C. The friction coefficient was below 0.06–0.08 with ZDDP, which is more than 20% lower than that without ZDDP and about a half of a steel/steel contact under the same condition. The formation of multi-layered tribofilm of 30–130
nm on the iron oxide was identified by TEM. The bottom part of the tribofilm is a layer of 10–30
nm that contains Zn, Fe, S, P, and O with a gradient composition, where distribution peaks of Zn and S were found by EDX.
Dilution of engine oil occurs when fuel is injected late in the combustion cycle to regenerate the diesel particulate filter used for trapping particulate emissions. Fuel dilution reduces oil ...viscosity and the concentration of engine oil additives, potentially compromising lubricant performance. Biodiesel usage may compound these issues due to its oxidative instability, and its higher boiling point compared to mineral diesel potentially causes it to concentrate more in the oil sump.
In this work, different amounts of mineral diesel and biodiesel (soy methyl ester, SME) were combined with 15W-40 CJ-4 diesel engine oil in laboratory oil aging experiments. Fuel was added and oil samples were withdrawn at periodic intervals. The oils were analyzed using typical oil analysis procedures to determine their condition, and wear evaluations under boundary lubricating conditions were determined using a high-frequency reciprocating rig (HFRR). Results showed that fuel dilution accelerated engine oil degradation, with biodiesel having a larger effect. However, friction remained unchanged with dilution, and wear actually decreased for fuel-diluted oils after 48 h of aging compared to aging without fuel dilution. Examination of the tribofilms by ultraviolet (UV) and visible Raman spectroscopy as well as Auger electron spectroscopy showed that additional carbon-containing components were present on tribofilms formed from fuel-diluted oils. These fuel-derived components may be responsible for the decreased wear observed.
PDF
