Tribological characteristics of two imidazolium-based room temperature ionic liquids (RTILs), 1-hexyl-3-methylimidazolium tetrafluoroborate, and 1-hexyl-3-methylimidazolium hexafluorophosphate were investigated under high vacuum conditions. Viscosity-temperature characteristics and thermogravimetric characteristics of these compounds were also investigated. Imidazoliumbased RTILs have relatively good viscosity-temperature characteristics that are comparable to those of multiplyalkylated cyclopentane (MAC). Thermogravimetric results showed that ionic liquids have high thermal stability and low vapor pressure. Ionic liquids showed low friction and low wear rate under high vacuum conditions, and high load-carrying capacity was observed.
The paper proposes a new model of chip forming process in three dimensional cutting with single point tool, in which the process is interpreted as a piling up of orthogonal cuttings along the cutting edge. Based upon the proposed model, an energy method similar to the upper bound approach, which enables to predict the chip formation and the three components of cutting force by using only the orthogonal cutting data, is developed. The method is also applied to predict chip formation and cutting force in oblique cutting, plain milling, and groove cutting operations.
One of the major obstacles in replacing the widely used zinc dialkyldithiophosphate (ZDDP) antiwear additive with a more environmentally friendly one is the difficulty of time-resolving the surface species resulting from its decomposition mechanism under high contact pressure and temperature. To tackle this issue, a newly developed miniature pin-on-disc tribotester was coupled with synchrotron X-ray absorption spectroscopy (XAS) to perform in situ tribological tests while examining the composition of the formed triboreactive films. The results showed that in the case of bare steel surfaces the initial decomposition products are mainly zinc sulfate species, which with further shearing and heating are reduced to zinc sulfide mixed with metal oxides. The mixed base layer seems to enhance the tenacity of the subsequently formed zinc phosphate layers composing the main bulk of the protective triboreactive film. This base layer was not observed in the case of coated substrates with hydrogenated diamond-like carbon (a-C:H DLC) coating, which results in the formation of less durable films of small volume barely covering the contacting surfaces and readily removed by shear. Comprehensive decomposition pathways and kinetics for the ZDDP triboreactive films are proposed, which enable the control and modification of the ZDDP triboreactive films.
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