Cold spray for high performance polymeric coatings – CARAPACE

In this research project, we start from two experimental results obtained recently: 1- ultra high molecular weight polyethylene (UHMWPE) coatings obtained by compression / sintering, provide an exceptional protection for the blades of marine propellers against cavitation erosion 2- preliminary results obtained at Tohoku University have shown that with the addition of nano-fillers of alumina, the cold-spray process allow depositing UHMWPE on metal substrates. Cold spray is a process consisting in projecting powder particles at supersonic speeds and typical temperatures below 400 ° C to obtain coatings. This process could be well adapted high-performance polymer to coat non-flat substrates such as blades pumps or propellers. An important market (boat propellers, rudders, pumps) might then be addressed in view to the considerable gain in lifestime (estimated at more than a factor 5) of such coatings. The main challenge lies in the fact that the properties of the coatings are not equivalent to that of the plates obtained by compression/sintering. At INSA LYON a Cold Spray device with improved performance is being installed. Our approach is twofold. By playing on the cold-spray parameters, we hope improving the quality of coatings by reducing the porosity, which improves the contact between grains, the powder density and finally the sintering itself. The key point is the thermomechanical cycle seen by the powder grains. We have the opportunity with the new device to vary the speed of impact, but also the temperature of the powder particles on impact. The powder particles will be then closer to their flowing temperature that should strongly optimize the sintering and thus the properties. On the other hand, a material research is needed to optimize the projected powders. We have already shown that the addition of nano-fillers could be important but we can also add other modifying (including PE maleic acid) here with the objective to improve adhesion with a metal substrate. The samples obtained will be analysed in comparison with the specimens compressed/sintered, first from a microstructural point of view (SAXS, WAXS, DSC, SEM, microtomography) with the main goal to understand and therefore to optimize both the process, but also the material. In particular we expect modelling and understanding the mechanical strength of these coatings against cavitation erosion (in relation SIMAP). In addition, a characterization of coatings on the cavitation tunnel of LEGI, we will first evaluate the resistance and therefore the lifetime of these materials but also to the mechanisms of damage. Finally, the polyethylene exhibits extremely high acoustic attenuation properties (typically 1000dB / m). This opens a second important application in the military field where the acoustic stealth is important. Indeed, these coatings could reduce noise radiated in case of cavitation, but more generally very broad frequency ranges can be reduced by coatings. These acoustic characteristics will be studied in detail in the laboratory LVA, but we also go further in characterizing the acoustic properties by acoustic microscopy. At long term, the cold spray process could lead to project other thermoplastic polymers paving the way for many other markets thanks to the diverse and important performances of these polymers.