![]() ![]() In the case of elastomers and polymers, photodecomposition or depolymerization can take place as well. The adiabatic cooling of the isochoric material causes (a) direct vaporization, (b) fragmentation due to supercritical relaxation, (c) phase separation and material ejection, or (d) phase transition without ablation. For USP lasers, in contrast to nanosecond lasers, the heating is isochoric. Subsequently, the lattice is thermalized by electron–phonon coupling. A further excitation by inverse bremsstrahlung starts an avalanche ionization. Electrons are initially excited from the valence band to the conduction band by single photon, multiphoton or strong field excitation. Generally, the laser ablation of polymers and elastomers is similar to dielectrics. #Lacona viii PatchIn this study, we aim to control the patch size-which has been identified as the most influential parameter-by direct ultrashort pulse (USP) laser microstructuring of the substrate. However, the tested substrate was “soft” aluminum and the smallest achievable patch size was 1 mm with 100 µm spacing, whereas patch sizes below 60 µm were found to unify good adhesion and CoF. Direct microstructuring was performed with a net mask. The latter method aims to passively influence the microstructure and is thus regarded as a subtype of microstructuring. The microstructure was related to substrate hardness and surface chemistry and roughness as well as coating conditions with preceding plasma treatment. #Lacona viii crackA dense crack pattern with small patches was found to enhance the adhesion and flexibility. Inherent to the coating process, resulting from a thermal coefficient mismatch of substrate and coating, is the formation of buckling cracks in the stiffer DLC. In particular, the microstructure of the DLC film has been attributed to adhesion and flexibility performance. Whereas the coefficient of friction (CoF) reduction in DLC coatings compared to their pristine substrate has been shown, the latter properties are subject to ongoing research. Besides the already mentioned properties of DLC, good adhesion and flexibility are mandatory requirements. Moreover, the viscoelastic contribution is reduced, though the former has been found to be more prominent. A hard, protecting, and low friction coating such as diamond like carbon (DLC) would significantly enhance the performance of dynamic rubber seals, as the adhesive forces between the rubber and its counterpart are reduced by interlaying a DLC film. Rubber seals are everywhere and, in every dynamic seal, the rubber is responsible for 50–70% of friction losses. ![]() ![]() The findings are ascribed to the relief of induced coating stress by the tile structure, meaning a more resilient coating. During continuous tribological loading, less heterogenous damage is produced for tile structured samples. Coatings with tile patterns did not experience a further fragmentation under load. Unstructured DLC coatings showed a crack pattern induced by the coating process, which was further fragmented by tensile stress. Tensile and tribology tests were performed on structured and unstructured samples. Rubber substrates were laser structured with tile patterns and subsequently DLC coated. In this work, a nature inspired approach is applied to render the stiff coating flexible and resilient to delamination at the same time by direct patterning. #Lacona viii freeThe elastic mismatch of rubber substrate and DLC coating prevents a fracture free coating application. Even though hard, low friction coatings such as diamond like carbon (DLC) would be beneficial for the performance and longevity of rubber seals, a crucial challenge remains. ![]()
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