Thermal spraying of cylinder bores with the Plasma Transferred Wire Arc process

Engine blocks of passenger cars made of hypoeutectic AlSi-alloys are generally equipped with cast iron liners in order to provide cylinder running surfaces that meet the tribological requirements. Thermally sprayed cylinder running surfaces are a promising alternative to cast iron liners. APS sprayed cylinder running surfaces made from low alloyed C steel have already proven their ability to reduce friction losses within the engine. Additional potential to reduce friction losses is offered by novel, and highly alloyed iron based surface building materials. This work describes the development of such materials and their application by the Plasma Transferred Wire Arc internal diameter coating process. The feedstocks lead to partially amorphous coatings with embedded boridic nanoscale precipitations if processed by thermal spraying. The coatings were applied onto the inner diameters of test liners made of aluminium EN AW 6060 and onto cylinder bore walls of an in-line 4 cylinder engine. Prior to coating, all surfaces to be coated were pre-treated by a novel fine boring process in order to create a surface topography which enables the adherence of the coatings. The coatings microstructures were analysed by light optical microscopy, hardness measuring and transmission electron microscopy. Furthermore the oil storage capacities of the honed surfaces were determined.