Technical advancements driven by performance
As the automotive industry continues to allocate considerable resources to improve vehicle fuel economy and emission standards, longer service life of the engine components has become an engineering priority. Further lowering friction and improving wear and corrosion resistance of piston rings was the ultimate aim of research work conducted within the RINGCOAT project. High velocity oxygen fuel (HVOF) thermal spray coatings were identified as promising candidates to replace hard chromium electroplating extensively used for meeting damage tolerance requirements. While current coating solutions become insufficient to withstand the stringent working conditions of piston rings, a newly developed steel coating with nanocomposite structure demonstrated a unique combination of excellent properties. In severe corrosive or abrasive environments, steel is rarely used since materials available are insufficient, leading to early wear and needing regular replacement to avoid seizure. Inasmet-Tecnalia researchers relied on HVOF thermal spray techniques to maintain the nanoscale structure of nano-sized amorphous powders. Complete particle melting could be avoided because of the high particle kinetic energy available during the HVOF thermal spray process. Furthermore, the rapid quenching of particles upon impact on the substrate was advantageous to the fabrication of high density coatings with lower residual stresses and improved metallurgical bonding. Piston ring prototypes with thermally deposited steel coatings have been evaluated in marine, automotive and motorbike engines, regarding their tribological performance. The new steel coatings with nanocomposite structure have shown both improved technical performance and cost competitiveness.
