Study of run-in behaviour of laser-patterned surfaces underdry sliding conditions

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The main goal of this proposal is to examine and to understand the evolution of laser textured surfaces, regarding topography and microstructure, in the very first sliding cycles in order to tailor friction and wear properties. The well-defined surface topographies will be created by laser interference metallurgy (LIMET). This technique allows for the production of highly controlled surface features in one processing step with lateral feature sizes on relevant engineering scales compared to those achievable using sequential laser texturing processes. Conventional technical surfaces are characterized by a stochastic roughness distribution which is difficult to describe in its entirety. In contrast to that, LIMET permits the reproducible formation of precisely-defined model surfaces and thus overcomes the stochastic roughness situation which is one of the major benefits within the project. First of all, a flat ball rubbing against a laser-patterned substrate will be scrutinized. In a next step, also the counter body will be laser-patterned and the role of mutual alignment and the lateral features sizes of the resulting pattern studied in detail. In this context, tests will be performed on technologically relevant materials (Ni, W, Ti), all having different crystal structures. Furthermore, the influence of grain structure (quasi-single crystalline and columnar-grown polycrystalline samples) will be investigated within the project.In addition, the experimental data will be used as input parameters for modelling the surfaces and microstructural evolutions in a direct collaboration with the Imperial College London (Prof. A.V. Olver, Dr. D. Dini and Dr. S. Medina). The research proposed by our collaboration partners in London addresses some aspects of surface interaction that are commonly neglected in contact analysis of real rough surfaces, specifically the interaction of the roughness of both surfaces and its relationships with normal-tangential loading interdependency and the influences of external loading mechanisms. Whilst much progress has been made in contact modelling without consideration of these subjects, currently allowing good prediction of loading stresses and contact conditions, it has now become necessary to introduce such details into the modelling system in order to reach the level of sophistication needed for fundamental and predictive modelling of friction and wear.The possibility to generate well-defined surface and the subsequent characterisation of the as-fabricated specimens by high resolution techniques combined with recently developed models by our scientific partners in London will lead to an enhanced understanding of interacting contact surfaces under dry sliding. Moreover, the microstructural degradation of the laser pattern will be extensively studied which can be directly correlated with the models. Finally, the gained results will be applicable to other materials and increasingly important nanoscale contacts.