Thermal Spraying comprises processes in which surfacing materials are heated to the plastic or molten state, inside or outside of the spraying gun, and then propelled onto a prepared surface. The substrate remains unfused. As surfacing materials, polymers, metals and their alloys but also ceramics can be used. The mechanism of bonding to the surface of thermally sprayed coatings is mostly mechanical interlocking. Thus, a roughened surface, characterized by numerous undercuts is essential to gain sufficient bond strength. For that purpose in general the surfaces to be coated are grit blasted prior to coating. The process chain in the production of coated cylinder bores consists of four steps. First is machining the cylinder bore to a certain diameter and then roughening of the surfaces to be coated. Next steps are the thermal spraying and the honing of the coated bore to receive a surface topography that meets the tribological requirements. Within this study it could be shown, that substrate roughening by fine boring with a geometrically defined cutting edge provides a good alternative to the commonly used grit blasting process in the automotive industry. Bond strength values of nearly twice the required minimum value of 30 N/mm(exp2) could be proved. Furthermore wire feedstocks were developed, that, when processed by Plasma Transferred Wire Arc spraying, lead to coatings with embedded, nano-scale boridic precipitations. In order to evaluate the SUNA feedstocks with regard to their tribological behavior, at the moment honed coatings are being tested on a reciprocating and on a rotating sliding wear tester against nitrided and also against electroplated, alumina reinforced chromium coated (CKS) piston rings.
Thermally sprayed nanocrystalline cylinder running surfaces in modern passenger car engines
Thermisch gespritzte, nanokristalline Zylinderoberflächen in modernen PKW-Motoren
2009
10 Seiten, 8 Bilder, 1 Tabelle, 8 Quellen
Aufsatz (Konferenz)
Englisch
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