Dry and Lubricated Sliding Behavior of Sub-Micrometer-Sized Suspension Plasma Sprayed Ceramic Oxide Coatings

Almost half of the energy produced by an automotive engine is dissipated by friction in the cylinders, the clutch, etc. In the context of reduction of the emissions of greenhouse gases (GHGs) to mitigate climate global warming (CGW) and of oil barrel price increase, reducing energy losses by friction is a critical issue. Surface treatments appear in such a context as never than before able to provide pertinent solutions to improve sliding behavior of mechanical parts. Numerous works have clearly shown that decreasing the scale of layer architecture below the micrometer scale was leading to an improvement of its tribological behaviors on terms of friction coefficient in particular thanks to improved mechanical properties, the toughness in particular. Suspension plasma spraying (SPS) appears as a thermal spray process able to manufacture thick (i.e., a few tens of micrometers) layers exhibiting a sub-micrometer-sized, and even a nanometer-sized one, architecture, while keeping the versatility and flexibility of the thermal spray routes; i.e., the ability to process a wide range of material natures onto a wide range of substrate materials of various geometries. This paper aims at presenting the tribological behaviors of several ceramic oxide coatings under dry and lubricated conditions, in terms of friction coefficient and wear resistance. Alumina, zirconia and composite layers are in particular considered. After a presentation of the implemented spray process and its operating parameters, the results show the benefit of decreasing the structural scale of layers in improving their tribological behavior, thanks to improved toughness.