Diesel engine development is continuously progressing: light vehicle diesel (LVD) engines are gaining in popularity in Europe and therefore we see a steady improvement in power performance and fuel consumption going along with increased loading of the power-cylinder components. Moreover, heavy-duty (HD) engines for trucks are facing stricter environmental legislation leading amongst other technologies to the introduction of exhaust gas recirculation (EGR). Whatever reduced emission technology will be applied, they all will significantly influence the engine tribology. This paper is dedicated to describing modern piston ring coating technologies to face the future diesel engine demands. The paper mainly focuses onto modern piston ring coating technology such as hard particle reinforced chrome plating, HVOF spraying and PVD. In particular, it will be discussed how thermal spray coatings need to be designed to find their position among established or future coating technologies of the competition.

The paper deals with an analysis of particle behavior in a HVOF-jet as a function of process parameters. The experiments were carried out using a commercial HVOF gun with hydrogen as fuel gas. A commercial 316 L stainless steel powder was used for spray material. The experiments were conducted by using on-line particle diagnostics in order to simultaneously detect particle velocity, temperature and diameter. The results were correlated with caught spray powder and splats. The experiments released that among many parameters the oxygen/fuel gas ratio is the most important parameter. It was found, that fragmentation of partially melted particles in a supersonic jet is not a neglectable phenomenon. It may cause excessive oxidation inflight and therefore is to be avoided in the production of oxygen-poor coatings. Furthermore, it was found that velocity or temperature measurements of particles have to be interpreted very carefully in order to characterize the process. Without taking a possible change of the particle size due to inflight fragmentation into consideration either measurement value will lead to very limited information benefit.

Quasicrystalline phases improve many alloy properties such as thermomechanical stability, thermal and electrical conductivity, and tribological performance. High hardness, however, is accompanied by brittleness, an undesired property in many applications. Reduced brittleness can be achieved by embedding quasicrystalline phases in a more ductile material, forming a metal-matrix composite that retains some quasicrystalline properties. This study evaluates thermally sprayed coatings made from different compositions of such composites. The coatings assessed were produced by arc-wire, HVOF, and atmospheric plasma spraying using various forms of feed material, including blended, agglomerated, chemical encased, and attrition-milled powders and filled wires. The investigation involved metallurgical analysis, proving the existence of quasicrystal content and assessing the matrix phase, and tests showing how sliding wear is influenced by the composition of quasicrystalline phases.