Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Automotive engine lubricants
(2019)
In 2003, ASTM Manual 37, Fuels and Lubricants Handbook: Technology, Properties, Performance and Testing, featured a chapter discussing automotive lubricants, including engine oils, automatic transmission fluids, manual transmission fluids, gear lubricants, and greases. This chapter, by Schwartz, Tung, and McMillan, surveyed all of these classes of lubricants, up to its publication in 2003.
More recently, the period between 2003 and 2010 has been addressed as part of a book copublished by ASTM and SAE International (coeditors Simon Tung and George Totten), where Fox surveyed the development of engine oil specifications that emerged during those years.
This chapter surveys the evolution of engine oil design and testing since 2002 and concludes with insights into future directions offered by recent tribological research. Our objective is to provide a reader new to the field with an understanding of the following:
- Engine oil composition and formulation
- North American engine oil specification development, and an outline of emergent European specifications
- How emergent specifications and legislative requirements are linked to the introduction of new engine hardware
- How tribological innovation can contribute to future enhancements in engine efficiency
In parallel, we will provide several tables comparing groups of contemporaneous specifications.
Carbidic Austempered Ductile Iron (CADI) microstructures containing eutectic carbides can be produced by the addition of carbide stabilizing elements, such as chromium. Carbides formed from the addition of Cr are eutectic of M3C type. The presence of such hard phases can enhance the abrasion wear resistance of ductile iron. A new CADI can be produced by the addition of Nb. Niobium carbide particles are formed in the beginning of solidification and remain stable once they are insoluble in solid iron matrix. The dry sand abrasive wear resistance of ductile irons alloyed with 1.0, 1.8, and 2.4 wt% Nb were tested in both “as-cast” and “heat treated” conditions using standard ASTM G65. Results were compared to abrasive wear data obtained on ductile iron alloyed with 1 wt% Cr, CADI (1 wt% Cr), and the basic composition of iron without carbide stabilizing elements. In the “ascast” condition, the addition of Nb did not lead to a reduction in wear, while CADI with Nb is a promising substitute for CADI with Cr addition, because both materials showed very similar values of abrasion resistance.
Micro-ploughing and micro-cutting mechanisms were observed on the worn surfaces of ductile irons. Abrasive wear resistance of these alloys was correlated with the volume fraction of carbides.
Force-distance curves have been recorded on thin films of lubricants. The lubricants wet the AFM tip, which causes a capillary force. This force depends on the shape of the tip, as well as on physical properties like viscosity and surface tension, which have been determined additionally with other methods. This way, their influence on the shape of the curves could be analyzed.
At the Stakeholder meeting of the EMPIR project “Multifunctional ultrafast microprobes for on-the-machine measurements”, details about two measurement modes were presented. Force distance curves and contact resonance measurements are compared. The basic principles are explained and exemplary measurements concerning mechanical properties of polymers are shown.
The motivation and the measurement setup for large fast-scanning piezoresistive cantilevers are presented. The theory behind the measurements of mechanical properties through contact resonance is explained. Results of such measurements on two kinds of polymer are compared to results from force distance curves. Noise, time-dependency and dependency of the results on the vibration mode are identified as challenges of contact resonance.
In the present work it was shown that the tribologcal profiles of special model oxides under dry unidirectional sliding have shown, that sub-oxides have a contribution to the tribological behavior of carbides and cermets, when they are tribo-oxidatively formed, because their tribological profiles as monolithic materials are homologous in part or totally, or compete with hardmetals or cermets, depending from the operating conditions regarded.
Oxidation effects on the functionality and formation of laser-induced periodic surface structures
(2019)
In the last decades, the formation of laser-induced periodic surface structures (LIPSS) has been widely studied, not only to stablish a general understanding of the main mechanisms present during the irradiation with ultrashort laser pulses, but also to identify the main processing parameters for its fabrication on various technical materials. However, an important and almost always present effect that is typically set aside is the material oxidation during or after the laser processing. Usually, this leads to optical, chemical, structural and mechanical alterations that are seldomly studied in detail. Therefore, in this work we present a study that includes the formation of LIPSS on Ti6Al4V alloy for tribological applications were different oxidations layers are involved.
The material characterization using different techniques, such as energy dispersive X-ray analyses (EDX), X-ray photoelectron spectroscopy (XPS), micro Raman spectroscopy (µ-RS), and depth-profiling Auger electron microscopy (AEM), and other techniques, confirms the formation of a non-negligible superficial oxide layer – strongly dependent on the specific processing parameters. We perform tribological experiments on laser irradiated samples oxidized by alternative ways to have a comparison on its friction performance. The obtained results show significant differences that depend directly on the thickness and the quality of the oxidized layer. This may open a fertile research area until now barely explored with clear impact on LIPSS based applications.
Renowned institutions in the field of tribology combine their testing and analytical capabilities with experts in materials/process information management technology to provide the respective Services in Europe (i-TRIBOMAT). This requires a centralized materials information management system or the standardised capture, consolidation and harmonization of tribological information.