Different processes permit to apply coatings in engine block bores. In this study, PTWA process and grit-blasting surface activationwere used.The layer is composed of iron in majority, oxides (around 20%) and pores (around 1%). The porosity in the coatings with 150 A torch is significantly higher in the middle and at the bottom of the bores,when compared to the 85 A torch. Very thick coatings of around 1 mm can be obtained without modification of the microstructure.The optimization of the surface activation by grit-blasting permits to have a reliable bonding strength at 40 MPa. Other processes are still studied such as laser texturation. Preliminary friction tests have been conducted with Cameron Plint tribometer and SPC machine. Results are promising with a
decrease of the friction if oil is below 100 °C when the matching elements are combined: the kind of lubricant and surface finishes of PTWA coating after honing step. A decrease of 20% can be observed compared to cast iron liner, form a current production engine. A PTWA coating with higher Ra and Rvk value shows lower friction than a smoother PTWA coating. The 0W30 oil use is better than with 5W30 one as the friction of the smooth PTWA coating is higher than the cast iron sleeve. But works are underway to test different rings in order to obtain the best performances. The next step is an electrical engine test without combustion but at high temperature with the complete engine block to assess more precisely the real friction mean effective pressure. Also, the influence of the surface profile on the bonding strength and the composition of the coating will be studied.