Patricia Iglesias

Liquid Crystals in Tribology

Two decades ago, the literature dealing with the possible applications of low molar mass liquid crystals, also called monomer liquid crystals (MLCs), only included about 50 references. Today, thousands of papers, conference reports, books or book chapters and patents refer to the study and applications of MLCs as lubricants and lubricant additives and efforts are made to develop new commercial applications. The development of more efficient lubricants is of paramount technological and economic relevance as it is estimated that half the energy consumption is dissipated as friction. MLCs have shown their ability to form ordered boundary layers with good load-carrying capacity and to lower the friction coefficients, wear rates and contact temperature of sliding surfaces, thus contributing to increase the components service life and to save energy. This review includes the use of MLCs in lubrication, and dispersions of MLCs in conventional polymers (PDMLCs). Finally, new lubricating system composed of MLC blends with surfactants, ionic liquids or nanophases are considered.

Wear of aluminium-base materials processed by mechanical milling in air or ammonia

Abstract The tribological behaviour of mechanically alloyed (MA) aluminium-base materials has been studied as a function of processing methods. In particular, a new sintered MA aluminium material, milled under an ammonia atmosphere (MA Al-NH 3 ) and consolidated by a single cycle of cold compaction and sintering, is compared with conventional MA aluminium (MA Al-air), milled in confined air and consolidated by a double cycle of compaction and sintering. The wear behaviour of the aluminium-base materials has been studied in a pin-on-disk tribometer, sliding against AISI 52100 steel pins. Dry wear tests have been carried out under variable load and temperature, to show that milling conditions, specifically milling atmosphere, have a strong influence both on mechanical properties and wear resistance. The higher wear resistance of MA Al-NH 3 with respect to MA Al-air increases with the severity of the contact conditions. Wear mechanisms are discussed from SEM observation of wear tracks, wear debris morphology and transfer tribolayers.

A Study of the Wear Behavior of Nanocrystalline Titanium Created by Large Strain Machining

Recently, it has been demostrated that large plastic strains imposed on a chip, during machining, results in significant microstructure refinement [1]. Titanium chip obtained by machining is found to have a nanocrystalline structure with ∼100 nm size grains. The hardness and strength of the nanostructures are seen to be substantially higher than those of microcrystalline titanium. In this work, the tribological behavior of this nanocrystalline titanium created by large strain machining is compared with that of conventional pure titanium. Tribological tests on titanium samples have been carried out in a pin-on-disk tribometer, sliding against AISI 52100 steel pins. The wear performance of the nanocrystalline titanium, is shown to be superior than the microcrystalline material. Wear mechanisms are discused from SEM observation of wear tracks, wear debris morphology and transfer tribolayers.Copyright

Neat Ionic Liquids and Additives in Lubrication of Steel-Aluminum

A series of seven room-temperature ionic liquids (IL) have been studied as neat and 1 wt% base oil additives in the lubrication of steel and aluminum contacts under increasing sliding speed, normal load and temperature. IL used as neat lubricants can produce, depending on the composition, tribochemical processes at the aluminum-steel interface associated with an increase in friction coefficients and wear rates. When IL are used as 1 wt% additives, surfaces interactions can give friction and wear values lower than those obtained for the neat IL. The lubricating performance of the additives is more dependent on contact conditions than on composition.Copyright

Characterization of Novel High Performance Lubricants

This work will provide a method to characterize a variety of novel high performance lubricants. In particular, surface tension and evolution of the contact angle on a variety of surfaces over one hour were recorded. Contact angles were measured using a rame-hart Goniometer. Surface tension is measured with the same device using the pendant drop method. Fluids studied here include: trihexyltetradecylphosphonium bis(trifluoromethyl-sulfonyl) amide ([THTDP][NTf2]), trihexyltetradecyl-phosphonium decanoate ([THTDP][Deca]), 1-ethyl-3-methyl imidazolium trifluorosulfonyl imide ([EMI][NTf2]), and 1-ethyl-3-methyl imidazolium trifluoromethanesulfonate ([EMI][FMS]). Contact angles were measured on the following surfaces: AISI 52100 stainless steel disks polished to 0.01–0.05 μm, Kapton, SU-8, Teflon, and glass slides. The resultant change in roughness on 52100 steel disks was measured to provide insight into the corrosive properties of each liquid.Copyright

Effect of Cutting Conditions on Dimensional Accuracy and Surface Roughness in Traditional Milling of Steel

Gear milling is one of the common gear manufacturing processes. In gear milling, the cutting edge of the cutting tool has an identical profile with the profile between gear teeth, and the cutting tool travels along the axial direction of the gear blank to produce the gear tooth by tooth. Due to the high requirements about the dimensional accuracy and the surface roughness during the gear manufacturing process, it is very crucial to understand the influences of cutting conditions on those requirements to improve the quality of the product and increase the production rate. In this study, a machined gear blank made from 1018 cold-rolled steel was subjected to variable speed and feed-rates in a traditional milling operation using a standard gear-milling cutter. The effect of the variable speed and feed-rates were analyzed by measuring the total lead (helix) error, total profile (involute) error, and surface finish of each gear tooth subjected to the variable cutting conditions. The objective is to experimentally investigate the correlation between the cutting conditions, i.e. cutting speed and feed, with the accuracy and quality of the machined surface during the gear milling process.Copyright