Open Access

In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Spikes produced at higher fluences and effective number of pulses per unit area present even thicker graded oxide layers that are also suitable for friction reduction and wear resistance. Ultimately, these femtosecond laser-induced nanostructured surface layers efficiently prevent a direct metal-to-metal contact in the RSTT and may act as an anchor layer for specific wear-reducing additives contained in the used engine oil.

In order to shorten time to market of products and to support new developments, the European Community is funding a HORIZON 2020 project called i-TRIBOMAT. In the field of tribology, renowned institutions combine their testing and analytical capabilities to provide the respective services. The later will be offered in Europe via a Single-Entry Point (SEP). Due to this combination of services, a testbed is created consisting of more than 100 tribometers. Thus, a large variety of testers exists, either commercially available or in-house built. Each tester is optimised to simulate a specific tribological contact situation. Currently, there is no standard available for the design of such testers. Especially, the way forces (normal load, friction force) and distances (e.g. stroke, linear wear) are measured, recorded and pre-processed differs from type to type. These forces and distances are essential for the determination of wear/ wear rates and coefficients of friction (COF), the core results of tribo-tests. This matter is complicated by the fact that e.g. for reciprocating motion, there are at least four different ways to determine COF. Depending on the testing conditions, these ways can lead to considerably different results. Currently, it is not obligatory to specify the method used for determining the COF. In order to make data comparable, there is a need for measures which ensure that each tribometer is delivering similar, at best the same results under the same test conditions, irrespective of its manufacturer, design, location, determination method and even operator. The way forward are improved Round-Robin tests. First results and other challenges faced by creating comparable tribological data will be considered in the present contribution.

In the present work it was shown the importance of the correct selection, implementation, and reporting of wear volume computation method and quanitifies the potential errors.

Renowed institutions in various European countries combine their tribo-testing as well as analytical and characterisation capabilities for the European Tribology Centre. This foundation of one of the largest Open Innovative Test Beds for tribological services, the aim of the European Horizon 2020 project i-TRIBOMAT, places certain demands on the comparability of the test equipment and execution process.

European tribological research organisations unify their capabilities for the European Tribology Centre (https://www.i-tribomat.eu/). At its core is a database, which data are made comparable and trusted via harmonised procedures for their generation. This contribution will focus on wear volume data.