J.L. Viesca

Lubrication of DLC Coatings with Two Tris(pentafluoroethyl)trifluorophosphate Anion-Based Ionic Liquids

The lubrication of a Cr-DLC coating with ethyl-dimethyl-2-methoxyethylammonium tris(pentafluoroethyl)trifluoropho-sphate [(NEMM)MOE][FAP] and 1-butyl-1-methylpyrro-lidinium tris(pentafluoroethyl)trifluorophosphate [BMP] [FAP] ionic liquids (ILs) as 1 wt% additives to a polyalphaolefin (PAO 6) was studied. Zinc dialkyldithiophosphate (ZDDP) was also used as reference in order to evaluate the effectiveness of the ILs. Reciprocating ball-on-plate tribological tests at loads of 20 and 40 N were performed. The results showed that both ILs exhibited a friction reduction, especially at the lowest load tested. Antiwear properties were also improved; the PAO 6 + 1% [BMP][FAP] mixture was slightly better, close to the values for PAO 6 + 1% ZDDP. Scanning electron microscopy (SEM) images and X-ray photoelectron spectroscopy (XPS) analysis indicated that the additive–surface interaction was responsible for the tribological improvement.

FAP − Anion Ionic Liquids Used in the Lubrication of a Steel–Steel Contact

Abstract This study compares the tribological behavior of two ionic liquids ([BMP][FAP] and [(NEMM)MOE][FAP]) used as oil additive for the lubrication of a steel–steel contact. Friction and wear experiments were performed using a HFRR test machine. Friction coefficient and electrical contact resistance were measured during the tests, and the wear surface was analyzed by confocal microscopy and XPS. The tribological results showed that both ionic liquids used as additive decrease friction and wear but the [BMP][FAP] had a better performance than the [(NEMM)MOE][FAP] due to its higher reactivity with the steel.

Effect of Shear Rate, Temperature, and Particle Concentration on the Rheological Properties of ZnO and ZrO2 Nanofluids

The rheological behavior of ZnO and ZrO2 nanoparticle suspensions in a polyalphaolefin (PAO 6) was investigated at high shear rates. Nanoparticles were dispersed at 0.5, 1.0, and 2.0 wt% in PAO 6 using an ultrasonic probe to produce nanofluids whose viscosity was determined over shear rates and temperatures ranging from 106 to 107 s−1 and 40 to 100°C, respectively. For the particle concentrations tested, the nanofluids exhibited a shear-thinning rheological behavior. The classical models typically used to predict nanofluid viscosity failed under these conditions because the viscosity depends not only on the temperature but also on the shear rate imposed. Two new experimental viscosity models were developed and validated for the studied nanofluids and constitute a practical tool to estimate the tribological behavior in lubricated pairs.

NiCrBSi coatings textured by Nd-YAG laser

This work presents and discusses the influence of Nd-YAG laser parameters on the texturing of a low laser absorptivity NiCrBSi coating obtained by diode laser cladding. In order to obtain statistical significance, different kinds of design of experiments were considered, choosing a central composite inscribed design as the best according to the number of factors and required runs. In the first stage, a diode laser is used to obtain the NiCrBSi coating and in the second stage an Nd-YAG laser is used to generate surface texturing. Finally, results are observed with a confocal microscope, obtaining diameter and depth of the dimples and statistically studied plotting Pareto charts and response surfaces. The study led to the following conclusions: higher energies and spot diameters generate dimples with larger diameters; low energies and shorter pulse duration involves greater diameters; at high energies diameters remain nearly constant versus pulse duration; at higher energies, shorter pulse durations show greater depths; and at low energies depth remains almost constant versus pulse duration.

Microstructure of NiCrBSi Laser Cladding Coatings Textured by Nd-YAG Laser

The use of texturing as a surface treatment that improves the tribological behavior is widespread in industrial and scientific fields, it is used in internal combustion engines [1], in biomechanical applications [2], in manufacturing processes [3] and in a full range of different applications. When texturing is carried out at low energy levels, the material melts superficially in a process governed by convection and thermocapillarity phenomena [4], whereas at high energy levels the reaction of the material could lead to its sudden vaporization [5] and local melting.Copyright

Tribological behaviour of microalloyed and conventional C–Mn rail steels in a pure sliding condition

This paper compares the tribological behaviour of microalloyed rail steel with conventional C–Mn rail steel under different test conditions (load, temperature and humidity). Pin-on-disc tribological tests were performed inside a climate chamber under different loads (20, 30 and 40 N), relative humidity (15, 55 and 70%) and temperatures (20 and 40 ℃). After the friction and wear tests, the worn surfaces were analysed using both confocal and scanning electron microscopies. The results obtained show that the use of microalloyed steel in railway applications under severe conditions (high loads and humidity) could lead to increased service life of the rails and could extend the time between maintenance operations.