The HVOF sprayed WC-CoCr coatings are widely spread due to their excellent resistance against wear and corrosion. These coatings are one of the most suitable alternatives for hard chromium in many applications. Within the research project, the most suitable hard chromium alternative for hydraulic devices in aircraft is being developed and tested. This application is highly demanding not only on the functional properties of applied coatings but also on the surface quality. Grinding and polishing of the coating are not sufficient, to achieve the necessary surface properties. This study aims to optimize the superfinishing process of HVOF sprayed WC-CoCr coating. The achieved surface quality is primarily measured using profilometry. With optimized surface preparation, the tested parts for aircraft hydraulic parts are treated and tested for leakage of operating fluids and high cyclic lifespan.

This paper describes an advanced three-dimensional surface finishing system for quantifying the surface finish of thermally applied cylinder bore coatings. The system can measure surface finish values over the total area of use with and without including the effect of porosity, as well as size distribution and percent area occupied by surface porosity. It can also quantify torn and folded material developed during the honing or grinding process, as well as hone angles in cylinder bores. The system provides a powerful tool for cylinder bore finish development and monitoring the effect of porosity on the finish of plasma coated cylinder surfaces. The paper also discusses the development of replicate material and the comparison of finish values developed through direct imaging and replication. Additionally, it explores the quantification of torn and folded material and crosshatch angles in the cylinder bore finish. Overall, the system improves the quality of finishing data and provides a time-saving solution for production or research and development environments.

In this study, two high-Cr stainless steel feedstocks and a post-spray honing process are evaluated for potential use on cylinder running surfaces in passenger car engines. The two materials, X12 CrNi 25-4 and X6 Cr17, were deposited by plasma transferred wire arc (PTWA) spraying on aluminum cylinder bore surfaces that were mechanically roughened prior to coating. The coatings were then honed to a mirror finish using progressively finer diamond tools. Coating surfaces were analyzed by SEM and REM imaging, roughness profiles were recorded, and coating hardness and porosity were measured. The results are presented and discussed along with recommendations for additional work.

The application of thermal coatings in cylinder bores is depending on above all functionality, process reliability and economy of pre treatment of the substrate surfaces. Different removing processes like water jetting or sand blasting are increasingly substituted by mechanical machining. Thereby great importance is attached to functionality and degree of automation. For an assured engine function, high bond strength is required. The roughening process as a modified cutting machining meets the requirements of modern production lines. Removing overspray after thermal coating by a water jetting process, is a further contribution for a higher automation degree. The final machining of sprayed surfaces is effected by a multi stage honing process. The composite structures of thermal coated layers call for high performance diamond abrasives. The finished functional cylinder surface comprehends cavities of thermal coated layer and smooth honing pattern. The technological description of roughening and honing, the process components as well as the machining results will be presented. Pre and post treatment are essential processes, which enable the application of high performance thermal coating materials in friction optimized combustion engines.

Anilox rolls require dense, adherent chromium oxide coatings capable of the highest quality microfinishing and laser engraving. Process economy and high deposition rate are also essential. Increasingly, anilox roll job shops are spraying such coatings using a high power plasma system, prompting this detailed investigation of processes, powders, and finishing. This paper evaluates how the material and the process influence the finished texture and engraving quality. Criteria for a successful coating are defined. The effects of plasma process, powder type, and coating microstructure on finish and engraveability mc analyzed in detail and practical recommendations are made. The test matrix includes high power and conventional plasma spray systems, three commercial chromium oxide powders used in anilox roll spraying, and three commonly used finishing methods.