Cinta Lorenzo-Martin

Bioderived Fuel Blend Dilution of Marine Engine Oil and Impact on Friction and Wear Behavior

To reduce the amount of petroleum-derived fuel used in vehicles and vessels powered by internal combustion engines, the addition of bio-derived fuel extenders is a common practice. Ethanol is perhaps the most common bio-derived fuel used for blending, and butanol is being evaluated as a promising alternative. The present study determined the fuel dilution rate of three lubricating oils (E0, E10, and i-B16) in a marine engine operating in on-water conditions with a start-and-stop cycle protocol. The level of fuel dilution increased with the number of cycles for all three fuels. The most dilution was observed with i-B16 fuel, and the least with E10 fuel. In all cases, fuel dilution substantially reduced the oil viscosity. The impacts of fuel dilution and the consequent viscosity reduction on the lubricating capability of the engine oil in terms of friction, wear, and scuffing prevention were evaluated by four different tests protocols. Although the fuel dilution of the engine oil had minimal effect on friction, because the test conditions were under the boundary lubrication regime, significant effects were observed on wear in many cases. Fuel dilution also was observed to reduce the load-carrying capacity of the engine oils in terms of scuffing load reduction.

Measurement of Thin-film Coating Hardness in the Presence of Contamination and Roughness: Implications for Tribology

Standard nanoindentation measurements on commercially available TiAlN, CrN, metal-containing diamond-like carbon, and TiN coatings, deposited on steel substrates were performed to determine coating hardness and elastic modulus. It was found that the coating surface roughness/morphology present after deposition can significantly affect the measurements of nanomechanical properties so that measurements of these properties on the as-deposited coating surface may be significantly different from the bulk. In addition, a surface measurement may produce a lower nanohardness due to the existence of a soft surface contamination layer. A simple method was developed to enable accurate measurement of the nanomechanical properties of coatings, while avoiding errors introduced by surface topography and the presence of superficial contamination layers on thin films. Friction and wear behavior, as well as the wear mechanisms in dry reciprocating sliding contact of the various coatings with a steel ball can be correlated to the surface attributes of each coating in terms of roughness and the presence of contamination layers, both of which are shown to also affect the nanohardness measurements.

Experimental Evaluation of Oxide Nanoparticles as Friction and Wear Improvement Additives in Motor Oil

The effect of two nanoparticle oxides on friction and wear was studied under laboratory test conditions using a reciprocating test machine and two test configurations. The addition of these nanoparticles in base stock oil under certain conditions reduced the coefficient of friction and improved wear, but that depended on the test configuration. Examination of the rubbed surfaces showed the pronounced formation of a tribofilm in some cases, while polishing on the surface was also observed in other cases. Contact configuration is important when oxide nanoparticles are being evaluated and the conclusions about their efficacy can be vastly different.

Influence of Surface Texture on Micro EHL in Boundary Regime Sliding

A hard steel ball was slid against textured coated and uncoated steel disks that had strongly directionally ground surfaces. The friction coefficient during ball-on-disk rotating low-speed lubricated sliding was continuously measured. The coefficient of friction rose from ≈ 0.12, which is typical for boundary lubrication regime, to as high as 0.45 whenever the ball was sliding parallel to the grinding ridges on the disc surface. The persistence of this “spike” in the friction was observed to be correlated with the hardness of the disc surface and the nature of the coating. We propose that the frictional spike is due to loss of micro-elastohydrodynamic lubrication, combined with side leakage, leading to intimate asperity-asperity contact. As a result, the coefficient of friction is close to that which is obtained there is no or minimal lubrication. This conclusion is supported by enhanced and persistent frictional spikes in tests conducted with discs coated with a very hard nitride thin film, and constant friction for a disk coated with hydrogenated amorphous carbon, which has low coefficient of friction when there is no/minimal lubrication.Copyright

Enhancement of Tribological Performance of 6061 Aluminum Alloy by Second Phase Hardening via Friction Stir Processing

The properties of metallic alloys can be substantial modified by the addition of a second phase particles. This is especially noticeable when hard particles are incorporated in a relatively soft matrix, often resulting in improved mechanical and tribological performance. This paper presents the results of our study on mechanical and tribological performance enhancement of 6061 Aluminum alloys by incorporation of B4 C particle via Friction stir processing (FSP). Unidirectional ball on flat friction and wear tests were conducted with a base material, friction stir processed 6061-Al and 6061-Al doped with B4 C particles via FSP against 52100 bearing steel balls under dry sliding conditions. The incorporation of particles not only reduced friction by 30% but also reduced wear by 2 orders of magnitude compared to unprocessed base and FSP material without particles incorporation. FSP alone without particles addition did not have a significant effect on the tribological behavior of the tested aluminum alloy.Copyright

X-Ray Diagnostics for Scuffing: Application to Phase Transformation in Nickel

Through the use of X-ray diffraction (XRD) and other diagnostics, the fundamental physical mechanisms of scuffing are becoming better understood. Peak broadening in the XRD pattern has been analyzed to determine the dislocation structure and crystallite size. Evidence from this technique has led us to conclude that scuffing is an example of adiabatic shear instability, wherein work hardening is exceeded by the thermal softening caused by the work. We are extending this research through scuff testing and XRD of nonferrous materials. For example, members of our team have recently found frictional behavior and surface morphologies consistent with scuffing in single crystals of MgO. Previous work has suggested the use of scuffing as a general method for the formation of metastable phases. Phase identification information available from the XRD data indicated the formation of austenite in scuffed SAE4340 steel, and the present work reports the discovery of a tribologically formed metastable phase in nickel. The formation of this phase was associated with surface roughening and a rapid friction increase of approximately 50%. However, the morphology of the roughened surface indicated abrasion rather than the gross plasticity typical of scuffed surfaces. X-ray diffraction identified the phase as either nickel carbide (Ni3 C) or hexagonal nickel, which are similar in structure, and ruled out the presence of crystalline nickel oxides. Analysis of peak widths revealed that the dislocation density in the areas that experienced a higher friction coefficient was lower than that in low-friction areas. This finding is not consistent with dislocation density changes in scuffed steel.Copyright