Steel cold spray coatings for cylinder blocks of internal combustion engines

CO₂ emissions related to piston friction inside the cylinders of automotive internal combustion engines represent about 0.5% of global emissions. This work presents the development of an innovative stainless steel – hard steel composite coating produced by cold spray, to be applied in cylinder blocks. Their surface finishing, by polishing or honing, reveals a surface with protuberances. During hot lubricated tribological tests, this topography interacts with ZDDP and MoDTC oil additives. Chemical reactions, activated by friction, form a thick tribofilm all around the protuberances, which ensures an extremely low friction coefficient and a full protection of the coating against wear, even under harsh friction conditions. The benefit in the boundary/mixed lubrication regime, combined with the one simulated in the hydrodynamic regime, are estimated to a 0.14% reduction of global CO₂ emissions, representing 50 MtCO₂ per year.