Engine blocks of modern passenger car engines are generally made of light metal alloys, mostly hypoeutectic AlSi-alloys. Due to their low hardness, these alloys do not meet the tribological requirements of the system cylinder running surface-piston rings-lubricating oil. In order to provide a suitable cylinder running surface, nowadays cylinder liners made of gray cast iron are pressed in or cast into the engine block. A newer approach is to apply thermal spray coatings onto the cylinder bore walls. Due to the geometric conditions, the coatings are applied with specifically designed internal diameter thermal spray systems. With these processes a broad variety of feedstock can be applied, whereas mostly lowalloyed carbon steel feedstock is being used for this application. In the context of this work, an iron-based wire feedstock has been developed, which leads to a nanocrystalline coating. The application of this material was carried out with the Plasma Transferred Wire Arc system. AlMgSi0.5 liners were used as substrates. The coating microstructure and the properties of the coatings were analyzed.

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The future development of motor engine design and technology governs the increasingly demanding requirements on materials in terms of friction and wear properties. In order to reduce emissions and achieve economical and environmentally sound solutions, thermal-spray processes became an interesting alternative to manufacture wear resistant and low-friction cylinder surfaces. Three thermal-spray processes are of major interest: twin wire arc system, high-velocity oxygen fuel and plasma transferred wire arc. The energy to heat the feedstock and the kinetic energy to accelerate the molten particles to the substrate differ within these processes consequently resulting in differing lamellar microstructures of the coatings. Hitherto, low-alloyed carbon steels with 0.1–0.8 wt% carbon have been successfully used for cylinder coatings. The motivation to alleviate friction losses is currently based on the material development of a new iron-base alloy with chromium and boron. This should solidify into a nanocrystalline or even amorphous matrix of high wear resistance. Prior to engine tests these coatings are characterized in laboratory by means of bench tests for adhesive tensile strength, tribological properties, and fatigue of the composite. Thus cavitation tests should reveal the tribological stability of these coatings and their ability to resist high-frequency cyclic impact stresses. The objective in this investigation is to describe the cavitation behaviour and the influence of voids like pores or oxides.

Future demands of diesel engines are about low-friction and wear-resistant materials in order to increase the efficiency and achieve environmentally sound solutions. Thus, thermally sprayed Fe-base coatings are investigated for application as cylinder running surfaces in cast aluminum crankcases. They should allow the desired combination of structural, productional, and topographical properties required in Diesel engines. To understand the influence of the characteristic microstructures on the integrity of the composites the coatings have to be examined in laboratory tests in terms of different loading situations. Cavitation tests were carried out where the tribological stability of these coatings and their ability to resist high-frequency cyclic impact stresses are revealed. Composite samples (base material and coating) were investigated in terms of crack initiation in a scanning electron microscope with an in situ 3-pointbending test. The endurance under cyclic mechanical stresses was tested with a 4-point-bending stress controlled test.