The impact of microstructural alterations at spray coated cylinder running surfaces of diesel engines – Findings from motor and laboratory benchmark tests

Future motor engine design and technology demand new materials that meet the requirements in terms of friction and wear properties. In order to reduce weight of the engine block and further more reduce the emissions thermal spray coatings are options to manufacture wear resistant and low-friction cylinder running surfaces. A motor cylinder with a thermally sprayed mild steel coating after a road test is prepared for transmission electron microscopy (TEM) investigations in the positions top dead center (TDC) and bottom dead center (BDC). In the dead centers of engines mixed/boundary lubrication conditions prevail. Within this study a new nanocrystalline thermal spray coating is investigated using two different laboratory tests where mixed/boundary lubrication regime is presumed. Conventional mild steel coatings and the new high alloyed Fe-base coatings are tested against two different piston rings in a reciprocating sliding wear test and an oscillating sliding wear test, known as SRV© test. TEM studies of the surface near microstructure demonstrate the difference in the microstructural alterations and wear mechanisms. Findings from the motor cylinder in surface and subsurface modifications are considered when discussing the results from laboratory tests in terms of initial grain size, influence of lattice defects and chemical influences due to oil additives.